Author Topic: Pottymill horizontal engine build  (Read 79613 times)

Offline tinglett

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Re: Pottymill horizontal engine build
« Reply #15 on: December 30, 2014, 03:35:18 PM »
Vince, Stew,

Thanks for the advice on the packing.  I tried out some PTFE tape and it seems to work great.  I have plenty of this stuff in the shop and chose to use some that is intended for gas lines since I don't ordinarily use the stuff anyway.  As you can see, it was trivial to form it into a rope.



It seems to work as smooth as the graphite, and was much less fussy to put in.  Of course less graphite may have been less fussy, too.  My graphite was stranded, and I think I could peel off a few strands to make it thinner.  It's messy, though, with all that graphite.  The gas line PTFE seems thinker than the usual stuff I've used for water pipes.  I may try the latter also when it comes time to tune up the engine, but I think what I've got will work as-is.

Todd

Offline tinglett

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Re: Pottymill horizontal engine build
« Reply #16 on: December 31, 2014, 02:03:25 AM »
Slower progress today with many distractions (i.e. kids :)), but I still managed to get the the majority of the valve chest made.

The Valve Chest.

Here is the plan for the valve chest.  I had to stare at it a bit to make sure I was thinking straight as the valve is off center.  I was thrown off course briefly because the passage holes for the cylinder (these are 12mm apart) are 3mm diameter, while those on the cylinder are 4mm diameter.  This is convenient as it gives me a bit of room for error.




The valve chest is 16mm square aluminum bar.  I opted to go with 5/8" this time, which is slightly undersized at 15.88mm.  I chose not to mill it square as the stock seemed pretty good as-is, and only one side really needs to be accurate to fit against the cylinder.  I figure I could lap that later if I must.  It was already undersized after all.  Here I am milling to the plan length, but I forgot to test it against the actual cylinder.  Fortunately it fit perfectly.  It could be undersized, but oversize will get in the way of the cylinder covers.


I needed to bore for the valve mechanism down the length of the valve chest.  I decided to do this on the lathe with my 4-jaw chuck and gave it the proper offset.  I centered it first, and then pushed it 8-6.35=1.65mm (0.065") to the back.  I noticed that the bar was a bit more than 1 thousandth thicker in one direction, so I chose to use that dimension for the offset.  If I lap it, this extra material will disappear.  Ok, I know it won't matter, but I'm just thinking through for future picky engines where it might matter :).


For an operation like this, I've been learning to pull out the drills I will need ahead of time, and I put all others away to minimize my chance of screwup.  Here the ducks are in a row in front of my lathe.  The plan calls for a 6mm hole, which is 0.236".  I was going to pull out a letter drill for this, but it occurred to me that 0.250 isn't that far off, and I have a reamer for that.  Actually, I'm using an under-reamer so it will be 0.249" and I'm hoping the valve will work just a little better for the effort.  The extra drill bit is 3/16" that I used for the initial hole.


Here's the slideshow of the operation.  Not exciting, but I took the pics so here they are.  Any tips are welcome if you see anything you'd improve if you were doing it.  The reamer did make a super smooth hole, but I know it isn't necessarily straight (i.e. I didn't bore it), and I'm also going to drill ports into it, which will mess up the inside.  Is there a better order of operations for that?  I could have drilled the ports first and then drilled this hole, I suppose, but then I'd have to worry about the depth of the ports (photos of that coming up).





There is a recess at the working end of the valve chest for a value guide.  This was 7mm so I chose a J drill bit to be the closest match.  This was to be 5mm deep, so I setup a dial indicator to measure the depth.  I need a better way to do this as my setup is pretty goofy.  I should probably attach a scale to the tailstock.


Next was time to drill the ports.  I placed the part in the mill with the valve passage down low.  This is the side that mates with the cylinder, and it makes sense the passage is further away so the mechanism clears the cylinder as it does its work.  I centered the part on the Y axis, located the end with the 7mm recess hole (the "working" end), and then located down X to the right position.  Fortunately, I had jotted down my conversions when I made the cylinder so I knew that this hole should be 0.625" from this end, and the next hole is 0.472" down the X axis.  I've been jotting these numbers, and even my conversions to full dial rotations plus extra ticks (remember I don't have a DRO), and that helped a lot here.


Here I skipped some photos to show the second port.  Note that the printing on the metal mates with the cylinder for orientation for future photos.


And here it is lined up with the cylinder.  Looks like a match!   Note that I picked a slightly large starter drill, which is why the holes in the valve chest look like that.  I decided it was close enough, and the next size smaller is quite a bit smaller.  It still constricts to 3mm (a #31 drill) for what that's worth.


Next I rotated the chest, keeping the working end to the right as in the previous photo.  I'll be drilling exhaust ports next.  These are spaced wider than the ports into the cylinder.


I ALMOST screwed up!  I left the part centered but at the last moment realized that the valve passage is now closer to the fixed jaw of the vice.  Doh!  Fortunately I looked down the end and noticed this.  Here I am locating the center which is 6.35mm from the fixed-jaw edge (rather than 8mm on center) and this is followed by a pic that shows it corrected.  These holes are 4mm so I used a #21 drill bit.



And I'll skip ahead to show the two exhaust ports.


Finally, I flipped it end-for-end so I didn't need to change Y.  This meant the working end was now to the left, so I measured from there to stay consistent.  This last hole is the intake port where the air hose will attach.  This is also a 4mm hole, so I used my #21 drill bit again.



And there it is.  I wish I could prevent the chuck jaws from scuffing it up like that.


Note that there are some additional holes that need drilling to attach the intake air fitting, the valve guide, and to attach the entire valve chest to the cylinder (a pattern of 8 screws).  I'll drill these when I make each part so they are aligned.  These will be teeny tiny screws and just a hair of alignment trouble won't be good at all.

Todd

Offline sbwhart

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Re: Pottymill horizontal engine build
« Reply #17 on: December 31, 2014, 06:26:11 AM »
Going good Todd

"And there it is.  I wish I could prevent the chuck jaws from scuffing it up like that."

Grip it with some shim from a cut up old drinks can.

Stew
A little bit of clearance never got in the way

Online Roger B

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Re: Pottymill horizontal engine build
« Reply #18 on: December 31, 2014, 08:30:52 AM »
Coming along well  :ThumbsUp:  :ThumbsUp: Your DTI on the tailstock looks fine to me. That's the sort of thing I do  ::)
Best regards

Roger

Offline tinglett

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Re: Pottymill horizontal engine build
« Reply #19 on: January 01, 2015, 01:58:54 AM »
I got a few teeny tiny parts made today.  I decided to call it a night considering it's the end of the year.  Happy new year! :)

The Piston Valve.

I decided the piston valve was next.  I'll fit it to the valve chest I made yesterday, and then use it as a guide to make sure all the other bits fit ok.  On starting this, I realized that I should make the valve rod first.  This is a 50mm rod threaded on one end to join with the piston valve.  The print calls for 3mm, so I went with 0.125" which is slightly larger.  The print called for a M3 thread for a length of 5mm on the end.  I decided to go with 4-40 thread which is very close.

You can see that I didn't need to turn down the rod much.


And here it is with the threads.  Easy enough.  It got a bit longer than 5mm, though, but fortunately I cut the rod a bit long just in case.  Looking ahead, I don't see this as too critical anyway.


Now I can make the piston valve.  Here's the plan for it.  There are so many dimensions it's a bit hard to actually see the piston in there.  It looks like a thread spool.


The piston needs to fit the valve chest which I reamed to 0.249".  So I pulled out some 0.250" rod and faced it.


Then I drilled and tapped a 4-40 hole to mate with the valve rod I made a few minutes earlier.  I did use a starter drill (not shown).  I wanted this to be pretty accurate depth, so I'm measuring with a DI again.



A test fit is good.


Next I drilled a shallow counterbore to fit the diameter of the valve rod, which is 0.125"  I just eyeballed the depth on this one.


It took a few test fits for this one.  The valve rod threads were a bit long, so I went to the grinder 2 or 3 times to shorten it up a bit until it fit just right as seen here.


Now it was time to turn out the spool area of the valve piston.  Here I slid it out of the chuck a ways, painted it with layout dye, and have measured in 3.5mm as called for by the plan.  I'm using my parting tool for this work.


Here I'm cutting part of the depth.  I'm mainly working on the right-to-left measurements.  It should be 3.5mm on each end with a recess of 8mm and an overall length of 15mm.  I nudged the cross slide to sneak up on it and made frequent measurements to get this as close as I could get.  Not difficult at all.


Now I have the length measured for parting off, but before I weaken that anymore, I'm ready to plunge to full depth.  Remember my 4-40 thread is on the right end.  This made me a little nervous as I went to the full depth...but it came out fine.


Here's full depth.  Nothing fell apart.  A good sign :)


I hit it lightly with scotch brite pad and filed the edges slightly (not shown) to get ready for a test fit.


And I did get a nice fit with the valve chest.  Not snug or loose.  Lucky.


Then I parted it off.


And here's the valve piston next to the valve chest.  I really need to clean up the ugly scratches on the valve chest :(.


Now I can finally provide a family shot!


The Valve Guide Stuffing Box.

The last part today is the valve guide stuffing box.  It fits in the 7mm counterbore in the front end of the valve chest and will hold packing around the valve rod.  The plan looks like this.  It's a real tiny part!


I had written that I made the counterbore with a J drill bit, which is 0.276, and is almost exactly 7mm.  The full diameter of this part is 8mm, so I found and faced a length of 5/16" (0.3125") brass rod and turned 5mm of it down to 0.276.



And then a test fit.  Umm....not so good.  I got a little too aggressive and should have checked it earlier :(


This was only 5mm of material so nothing really lost but some time.  I parted off the scrap and tried again.  This time success!


Next I drilled for the 0.125" valve rod.  I'm working from the bottom of this part right now.  Note that the top has a 8mm rim to it.



I got a very nice fit as far as I could tell at this point.


Next was time to part it off and turn it around in the chuck and face it.  I chucked it snug, but not too hard.  I don't want to mess up the fit too much, but jaw marks won't be seen at least.



Now the fun part.  It needed to be drilled out 6mm for a 5mm depth.  This had me worried...not much material left after that!  Here I used a starter drill which was already a pretty large fraction of the material.


The 6mm hole was going to be made with a B drill bit.  I held it up to the started hole and decided I needed to have the starter drill do a bit more countersinking.  I didn't want the B drill to wander too much.  There simply isn't much room to wander.  Here's a pic of better use of the starter drill.  Somewhere I was told to always get a little of the countersink going so a drill bit can follow better.  That seems logical to me.  Here I wanted as much as I could get.  It's almost exactly 6mm.


And here I do the drilling with a DI.  Can't go too deep either!


There's the little guy.  Not much weight left of the little brass that went into it.


And here's the fit in the valve chest with the piston valve installed.


That's all for today.  I know I posted a LOT of pictures and I hope they are useful for somebody.  Tomorrow I will make the valve rod guide that fits into this stuffing box, the air connection fitting, and the valve chest end cover.  We'll see if I can get them all done, and that will finish the valve chest assembly.  This assumes I don't party too much tonight :).

Todd

Offline b.lindsey

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Re: Pottymill horizontal engine build
« Reply #20 on: January 01, 2015, 02:46:42 AM »
You are making great progress Todd. Once you get done with all the holes in the valve chest, a little time on a surface plate with some 320 or finer grit sandpaper will smooth things out and likely  remove most if not all of the scuff marks. I often leave a couple of thousandths of extra material just for that purpose.

Still following alone and enjoying the build.

Bill

Offline tinglett

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Re: Pottymill horizontal engine build
« Reply #21 on: January 03, 2015, 03:33:22 AM »
I'm getting behind with the documentation.  Here's a tiny update, and I'll get more written down tomorrow.

The Valve Chest End Closure

It doesn't get any easier than this.  The valve chest was drilled and reamed all the way through.  The back end needs to be covered up.  It's a simple aluminum cover.

The cover is to be 8mm in diameter.  I faced off some 3/8" Aluminum rod.


I turned a length down to 8mm, which is 0.315".  Only 60 thousandths to remove.


Next I turned a bit more to fit into the valve chest.  I had reamed this to 0.249" so I snuck up on it and tested until I got a tight fit.



And then parted off.  I pretty much eyeballed these thicknesses.


And there it is.  Not much to look at.


But...it makes a nice little SNAP when I press it into the valve chest with my fingers.


More exciting stuff tomorrow...

Todd

Offline tinglett

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Re: Pottymill horizontal engine build
« Reply #22 on: January 03, 2015, 07:27:01 PM »
The Valve Rod Guide

Next is the valve rod guide which slides into the valve guide stuffing box I had made earlier.  Here is the plan, and recall I decided to use 0.125" rod for the valve rod since I'm working partly with imperial measurements in my shop.



I also decided to use 2-56 "bolts" for attaching it.  I haven't made threads for something so tiny before.  I also needed to create the shape.  I've seen reference to "filing buttons" many times on this board and thought I'd make my own attempt at making some to see how it goes.  The part is very small, so I figured filing wouldn't take long.

The part is 8mm by 15mm so I found some 3/8" by 5/8" brass bar which was darn close.   Here I am indicating it in the 4-jaw.  I've been using the 4-jaw a lot and getting pretty good at doing this :)


With an interrupted cut, I used a pre-made carbide cutter.  If I wreck it, I'll just throw it away.  But it was no cause for alarm.  It faced just fine, though a bit rough with this cutter.


I then turned to diameter to fit the valve guide stuffing box I had already made.  I switched to my parting tool to get a nice shoulder.



Doh!  I went too far again.  You'd think I'd learn.  I parted off the waste, but left a little bit as a reminder of what "too far" looks like.  This time went fine and I got a good fit.




I cleaned up the shoulder and parted off the excess to match the plan.  It is designed to stick out a bit.



Next was time to drill out the passage.  The plan calls for 4mm, but my valve rod is 0.125" so that's what I used.  I estimated the depth knowing my tailstock runs 1/16" per crank.  That's good enough because I'll part off the excess anyway.



A test fit of the piston valve and rod for sanity.  Looking good.


Next...part it off.  This actually went way better than I thought it might, considering the interrupted cut.


I turned it around and chucked it to face it, rather than file it.  This is the side you'll see, so I wanted it to look nice.  If I couldn't reliably chuck it, I would turn to the file, but it worked fine.



There it is...nice fit, but I still need to shape it.


Before shaping it, I wanted to drill the holes for bolting it to the valve chest.  Here I have chucked it in the mill and am using a 0.125" drill bit to center it under the chuck.


I used a #50 drill for the 2-56 tapped hole and a #43 for the clearance hole in this part I am making.  I measured depth with a DI again.




The tap was so fine, and I was working with "gooey" aluminum, so I decided to tap completely by hand.  I had already drilled the brass as a clearance hole, so that worked as a guide to help me hold it straight.  Note that I didn't even use the t-bar in the tap wrench.  I could easily twist it with my hand and was very paranoid about it.  I did the other side the same way.


Once I could remove the clamp, I used the tap once more to clean it out and go a little deeper.  I did this by hand again, rather than chucking it into the mill's chuck as I usually do.


Filing Buttons

I have to admit, I've seen filing buttons used in posts here on MEM, and perhaps on other websites, but have never seen them mentioned in books, and I've certainly never used one.  So from here on I'm making this up as I go along.  Suggestions are more than welcome.

The first buttons I made were spacers for the bolt holes I just made.  The plan suggested a 2.2mm radius, a 4.4mm diameter which is 0.173".  I had some 3/16" (0.188") steel rod handy, so I drilled and tapped a length of it.  I tapped for 2-56 to match the bolt holes in the part.



I used the chuck in my tailstock as a guile for hand holding the tap.  I found if I opened the jaws just right, it guided the chamfer of the tap wrench perfectly.  I know I should drill a hole in the tap handle and use a center, but this worked fine.  It was a little harder to turn the tap in steel...but surprisingly not much.  If it started getting tight and felt like the tap might distort, I unscrewed it, cleaned and re-oiled it, and went at it again.  Worked good.


Then I parted off two of these.   My first two buttons!


I drilled for a clearance hole and parted off two more buttons from the same rod.



Here are my two sets of buttons.  I really only needed one set, but I thought it might be handy to have an extra.  I'll use them both for filing this part.



For the center button I could see two problems.  First, I could only place a button (realistically) on one side.  No big deal...less work in fact. But the other problem is that space is tight.  I can only fit a sliver of a button in the middle.  But that's ok.  This needed to be 8mm diameter which is 0.315".  I decided 3/8" (0.375) was close enough.  To provide clearance for the side buttons I just made, I clamped the rod in a vice and made some flats by eye using the mill.  I need to work on my eyeball skills...it was a little off.  I drilled it for a 0.125" hole to match the part.





And here's how this button fits on the part.  I realized I could rock it back and forth to help guide more on the side I was currently going to file.  Cool.


Now on to filing.  I clamped it in a mini-vise and filed down the big chunks, trying not to actually touch the buttons.  This went pretty fast.  The hard part was finding spots for the vise to get a grip.


I switched to a finer file and found that for the fine work it was easier to slide the part over the file than to move the file.  Here I am done with one side.


I repeated with the other side.  This was going better than I imagined.  It was pretty easy to feel when the file started biting into the button.  The buttons weren't loose, so they wouldn't spin, nor were they hardened.  So I had to be careful.


A little touch-up with 320-grit sandpaper and I declare the part came out pretty darn good!


And here is how it fits into the valve guide stuffing box.  I'll show the bolts later.


Next up is the air connection.  This part looks very similar to the valve rod guide in this episode and I approached it more-or-less in the same way.

Thanks for checking in.  I'm pretty happy with how the filing worked out, but I'm still looking for any advice on how to do it better.  Or maybe just how to do it in a different way.

Todd

Offline ths

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Re: Pottymill horizontal engine build
« Reply #23 on: January 03, 2015, 09:18:24 PM »
Great use of the filing buttons Todd. I'd never seen that particular method for shaping flanges before,, the end result looks great. Hugh.

Offline b.lindsey

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Re: Pottymill horizontal engine build
« Reply #24 on: January 04, 2015, 01:23:23 AM »
Still looking great Todd. You are making some good progress...keep the updates coming :)

Bill

Offline tinglett

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Re: Pottymill horizontal engine build
« Reply #25 on: January 04, 2015, 04:48:07 AM »
The Air Connection

This part looks very similar to the valve rod guide, and I made it pretty much the same.  Here's the plan for it.



I decided I'd make the part as shown, but I'd also drill and tap it for 10-32 threads so I could add this fitting that I've used with my previous three engines.  The passage through this fitting is a bit larger than 2.3mm so I hope it will deliver enough air.  It's very convenient with the quick disconnect feature.


I didn't happen to have any brass bar stock 1 inch wide, but I did have some 1 inch rod so I started with that.   I faced it, turned it down to the 8mm outside diameter which is a purely decorative measurement, drilled it through with a #39 drill for the 2.5mm hole, and then tapped it for 10-32 threads.







I tested the quick disconnect fitting and it worked fine.


I parted it off, then flipped it around and turned down the protrusion that fits into the valve chest.  It needed a little cleanup, which it got.  For the cleanup, I applied some layout dye because I had already gotten a nice fit and I wanted to see easily if I was skimming off any additional material.  I didn't bother trying to get a crisp shoulder.  Instead, I decided to apply a slight chamfer to the valve chest to make clearance for it (not shown).



The fit was good.


Next I moved it to the mill and centered the chuck on it by chucking the fitting.


Then I drilled and threaded the mounting holes.  I decided to use 3-48 "bolts" for this.  I threaded entirely by hand as I did with the valve rod guide even though these threads were slightly bigger.



Now I could screw it down with a temp screw.  Previously I held it by hand, though it was snug in the valve chest, but now I couldn't let it move.


I drilled and tapped the other side, and then tried the real bolts.  Looked good, though isn't the right shape yet.


I found a washer that fit underneath.  I'll used this to space it away from the valve chest and milled away a bunch of the material.  I didn't get fancy and try to mill diagonals, though, although I suppose I could have tried.





I machined a filing button to fit over the 8mm diameter side.  Since this side is tapped, I'll simply attach it with a 10-32 screw.  Well, a nice plan, but I found my screws were all relatively long so I had to get creative with a pile of washers.  It worked ok.




I made a single filing button for one of the other holes.  There wasn't room on the top side for it, so I attached it on the back side.  The screw head still interfered with the large filing button, so I had to turn a little relief it that button.  I gave this little button threads as the 3-48 nuts I had on hand were larger than the button.




With buttons on one side only, and different sides at that, I had to file carefully.  They didn't turn, nor were they hardened.  So I started filing.  Here's one side rough filed.  It only took 10 minutes...maybe less.


And here's the other side.  I see I got a little too aggressive on the first side, but it wasn't too bad.



Here's it's done, though it needs a little cleanup.  The "bad spot" is on the right low side.  It jumps out at me, unfortunately.


But it looks pretty damn good installed on the valve chest :).


Another part checked off the list.  Thanks for looking in!

Todd

Offline Stilldrillin

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Re: Pottymill horizontal engine build
« Reply #26 on: January 04, 2015, 09:27:07 AM »
But it looks pretty damn good installed on the valve chest :).
Todd

The whole assembly, is looking, "pretty damn good", Todd! 

Well done, and well shown.......

David D
David.
Still modifying bits of metal... Occasionally, making an improvement!
Still drilling holes... Sometimes, in the right place!

Online Roger B

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Re: Pottymill horizontal engine build
« Reply #27 on: January 04, 2015, 12:34:58 PM »
Good progress  :praise2: I like your solution to making two bolt flanges  :ThumbsUp:  :ThumbsUp: I used a jig on the rotary table, that was probably too complicated  ::)
Best regards

Roger

Offline tinglett

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Re: Pottymill horizontal engine build
« Reply #28 on: January 04, 2015, 10:46:58 PM »
Attaching the Valve Chest to the Cylinder

I wrapped up last night drilling the valve chest for attachment to the cylinder.   There's good news and there's bad news.  This post is the good news part.

The valve chest is attached with 8 screws in a 2-row of 4 screw layout.  I didn't want to mess this up.  I also wanted a reliable process for position and depth since I don't have a DRO.  In particular, my mill is HORRIBLE for Z depth, so I need to resort to a DI always.  I thought I'd try to setup some stops for reasonable consistency and no fuss readings.  The process went well.  Here's what I did.

I first devised a means to clamp the valve chest and cylinder together.  This looked like it would work.  I had paper on the left side which is hard to see in this photo.  Is paper needed on both sides?


I disassembled the clamp, painted the top of the valve chest with layout dye and scratched in the layout with my caliper, then clamped it up again.  I haven't been doing layouts like this lately, but since I'm using dials and these parts have a lot of work in them, I thought it best as extra assist against screwups.


I planned to use 2-56 screws that are 3/4" long.  That means they'll only grip with 1/8" into the cylinder.  I decided to drill 3/8" into the cylinder in case I wanted to go with slightly longer screws.  That means using a #50 drill for the hole all the way into the cylinder, and then opening it up with a clearance hole with a #43 drill only in the valve chest.  I'd need to switch drill bits, so if I'm using a stop I'd need a way to replace a bit reasonably accurately.  I found a length of aluminum rod to use for this purpose as shown in the picture.


Next, I brought down the drill with the mill powered off so it just touched the cylinder.  Note that I've removed the valve chest.  This is the depth of the valve chest and is where I want to stop the larger #43 drill.  In the following photo I show that I set the stop with a block of 3/8" aluminum.  The working theory is that if I drill to the aluminum block I will drill completely through the valve chest and reach the top of the cylinder.  If I remove the aluminum block I will drill 3/8" deep into the cylinder.



Now I need to locate the position of the first bolt.  I wrote relative distances, including turns of the dials, on a nearby piece of paper.  Trying to reduce the screwups.  Fortunately, even with the stop in place I was able to reach the top of the valve chest in order to use the starter drill shown.   Lucky me.


It was a matter of repeating 8 times:  a) locate to position along X with Y locked;  b) use starter drill;  c) insert #50 drill using aluminum rod spacer with mill head completely raised; d) drill to full stop depth (into cylinder); e) insert #43 drill using aluminum rod spacer with mill head completely raised; f) drill to depth using extra spacer block.   It was step f that had me worried.  But somehow I never forgot that extra spacer block.



I repeated this for the first series of holes down the X axis and kept the Y locked.


Then I had to crank it back and account for backlash.  Remember I'm using dials.  I lowered the drill into the first hole with the mill powered off to double check. It was aligned.



It occurred to me before I started moving down X that I needed to adjust for backlash again because I was changing direction.  I lowered the bit back into the newly drilled hole and turned the dial to get rid of it and reset to zero.  All was well and I finished the second row of holes.  Maybe it would have been best to do the second row of holes in reverse.  The layout lines where helpful to give me confidence I was hitting the right spots.


With all the holes drilled, I removed the clamp and valve chest and tapped all the holes by hand.  This was actually very easy.  There is very little resistance to a 2-56 tap in aluminum.  I had to be careful not to strip any threads I created.  While I was at it, I measured the hole depths and they varied by only 6 thousandths.  I was surprised by that.


I'll switch to hex head bolts, but for now I screwed it on with these screws.


The next installment will document what isn't going so right.  Stay tuned.

Todd

Offline tinglett

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  • Rochester, MN, USA
Re: Pottymill horizontal engine build
« Reply #29 on: January 05, 2015, 12:25:54 AM »
A Visit from the (self) Inspector

Inspection didn't go so well today.  Everything was looking pretty good, though as I looked closer I could see the valve chest was a little extra long.  That's why the cylinder covers weren't pressing down perfectly.  That'll be an easy fix...but I'll wait a bit.  I found (and created) more problems :(.

First, I was assembling the engine and noticed filings inside the cylinder.  What?  In my haste yesterday to make room for longer cylinder chest screws, I realized I hadn't completely analyzed the situation.  The screw holes I just drilled were peeking into the cylinder!  Damn.  I would have needed to be 1/16" shorter or so to avoid this.  If I had stuck to the original plan of 1/4" depth rather than 3/8" I would have been fine.  Sigh.  I cleaned it up and I don't think these will be a problem as they certainly will be sealed, and I could put some kind of goop down the holes to be sure.  It's the added friction I don't care for.  I think I'm going to leave it as-is.  At least they can't be seen without X-ray vision :)


Next, I noticed the valve piston would not move all the way across the valve chest.  There was a bit of material from a recently drilled hole (correctly drilled, at least).   As I pushed out the valve piston, it broke!  Blech.  I was worried about that spot.


Time to make a replacement valve piston.  I was cutting the first groove and it chattered and bent.  Blech #2!  The photo doesn't look bad...but it really is bent badly.  I've been having trouble parting again as I'm getting used to this new AXA parting tool holder.  I think my main problem is that it is angled up and I probably need to change the angle on my parting blades.  In this case the blade was riding just a little too low.  Fixed now, but not in time for this part.   I did manage to create a new valve piston, though.


Here are a couple pictures of the full assembly.




Finish needs to be cleaned up.  I need to shorten the valve chest by 0.003" on each side.  I should probably replace the piston rod, and maybe the valve rod, as they've gotten beaten up as I've worked with it.  The trouble with both is that they are pretty tightly wedged into their corresponding pistons.  I haven't used locktite, so this is fixable.  If they really cause trouble, I can always re-make both rod+piston to solve this.

I was also able to test the cylinder.  I gave it 30 psi of air, while holding onto the valve chest end cover, and moving the valve back and forth will snap the cylinder back and forth.  The piston is a bit "sticky" on the far end, which I believe is due to the rough scrapes on the piston rod that is visible.

Now for the bad news, and Stew maybe already caught this.  I've somehow managed to swap the intake and exhaust sides of the cylinder chest!  Crud.  Note the flat is on the top side of the cylinder.  When I rotate it over, the intake will be facing down.  That's the result of a beginner reading a plan.  So I believe I have 3 options:
  • Gravity won't affect the air, so leave it as-is :).  I'll likely go with this option, but I don't think my fitting will be reasonable in that space.  I'll need to make an elbow, which actually might look nice.  But I'll have these two exhaust holes in plain sight.  What could I install around them to make it look like I am routing the exhaust somewhere?  Anyone of thoughts on that?  maybe an idea from another engine?
  • Rotate the cylinder end-for-end.  This means my engine would be a mirror image of the original design.  That is, it would look like the last photo, except the cylinder flat would be on the bottom where it needs to be.  I'll need to think through what a mirror image of everything means.  It would probably be fine, but more chance for me to mess up a future step as I adapt to that.
  • Remake the valve chest.  There are many holes to line up and fittings to mate them.  This feels like starting over and is not likely to happen.

One other detail for idea #2 is that I'll need to be able to attach the parts in the flipped around position.  I checked this and found the valve chest does screw down fine in the reverse position (woot!), but my holes are ever so slightly off for swapping the end covers.  They are close, so I think drilling the covers for one size larger clearance hole would do the trick.

I'm leaning heavily to the first option.  I'll whip up an elbow of some sort for the fitting and see how it looks.  But I don't have great ideas for something to go over the exhaust holes.  I could make two flanges, or a single big flange of some kind.

Todd

 

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