Author Topic: Pottymill horizontal engine build  (Read 79560 times)

Offline tinglett

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Re: Pottymill horizontal engine build
« Reply #105 on: March 22, 2015, 03:03:53 AM »
Marking out the flywheel (part 3 -- the last part!)

Hopefully this detail will be helpful to someone.  I'll keep plugging along.  I really did learn a lot going through this.

In the last installment I had just shifted the Y axis and rotated the RT to get into position for an outer cut for the spokes.   For today, my MILL IS UNPLUGGED and I'm only scribing.  So my "cutters" are zero radius, I suppose.

Looking at the photo below, the position seems good.  The Y axis was pulled back toward me by 220 thousandths in the last installment, which is why I'm on the back side of the spoke line, and the RT is rotated (effectively) -4.61 degrees.  I know it's hard to see direction in the photo, but if I move along the X axis I will scribe from the outer edge of the hole to the outer edge of the other hole.


I didn't want to scribe if my math (or thinking) was screwed up, so I shifted X to the other hole and found it was spot on.


So I scribed it...


The software, either Marv's or mine, doesn't report where to start and end in X.  I'll maybe add that to mine for reference.  When cutting for real the holes will be real holes, of course, and I think it would be wise to use an end mill with a slightly smaller diameter than the smaller hole.  Then the start/end positions for this cut won't be so critical.  But it may still be handy to have the numbers to get them close.

Now the cool thing is that I can advance to the next position simply by rotating the RT 72 degrees -- the spoke angle for this 5 spoke flywheel.  That's 18 full cranks on this RT.   The problem is that I didn't dare mess with the dial.  I really would have liked to zero it out, but I don't want to re-find the real zero later.  So this meant counting out full turns and finding that 3 + 23 minutes + 20 seconds finishing spot each time around.   It was fairly tedious, but there were only 4 more turns so it wasn't so bad.









Now I had to readjust for the other side of the web.  This meant dialing Y forward by 440 thousands (twice 220).  I used the grease pencil mark to reassure me I got this right.  It was forward so there was no backlash to deal with.



I dialed the RT forward to 4.61 degrees which is 4 degrees 36 minutes 36 seconds.   This time I got the crank positioned right.  Or at least I think I did.  See the photo.  The 4 degrees is a full turn so I ended up past the 0 on the dial.  I advanced forward 3 big ticks (30 minutes) and 3 more smaller ticks (+6 minutes).  Then I had to advance forward until the +40 tick on the vernier lined up.  That's hard to see in the photo, but it's the 2nd tick past the 0 on the vernier (left) side.



Now that I can run the dial properly, the rest was easy.  Trace out 5 more edges.  I alternated the direction I scribed out of laziness.  With a real cutter I wouldn't do this.







Note in this photo that I somehow managed to scrape an arc in the lower right area of the photo.  I'm not sure how I did that, but perhaps I didn't pick up the scribe fully when I cranked to the next position.  I need to be more careful.




And now we are almost finished.  As I'm using real cutters I'll probably do this in two or three passes.  To do this, I think it's simply a matter of moving Y a little further out.  Instead of 220 thousands, I might use 225, and then take the last 5 thousandths as a second pass.  I'd do this by going around all 5 spokes at 225, and then going around again at 220.  Seems reasonable.

Note that rogue arc on the left side.  I decided not to "fix" it.  But don't confuse it with the outer arcs I am about to make.


I just have to produce the arcs on the outer edges of the webs.  The first step is to center again.  All I had to do was crank to my grease pencil mark and dial to zero and it was done (only showing X here).  Very cool.  Thank you That Lazy Machinist!   I imagine this is a common trick, but it was new to me.



To make the arc I had to dial out to the outer edge of the outer holes.  That's easy math.  My outer holes are centered at 1.4375.  The hole diameter is 0.188 which has a radius of 0.94.  So add them together and X=1.5315 is what I want.  Start/end is easy too, as these are angles.  The total span between spokes is 72 degrees.  The hole starts at 8 degrees and ends at 72-8=64 degrees.  Another way to look at this is that I need to advance 2 cranks (8 degrees), draw the arc for 14 cranks (56 degrees), and crank two more cranks to align with the next spoke.  Very easy.

Here's the first arc.  My scribe was getting dull :(








And that's it!  Like the inside cuts, I think I'd do the arcs in two or three passes.  That's just a matter of adjusting X three times and going once around for each setting.

I think I've got this down.  Now I need to do some trepanning to form the rims and hub.  I'll do that on the lathe, and I think I'll make the flywheel a bit more thin.  Right now it is over 1 inch wide.  I'm thinking it maybe should be 3/4 inch wide or so.  Anyone have opinions on that?

Thanks for following my arduous journey.  I learned a lot.

Todd

Offline ths

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Re: Pottymill horizontal engine build
« Reply #106 on: March 22, 2015, 09:07:02 AM »
Hi Todd, that's a very instructive and detailed post, and a very useful one at that. Many thanks, Hugh.

Offline vcutajar

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Re: Pottymill horizontal engine build
« Reply #107 on: March 22, 2015, 11:24:11 AM »
Todd, that was an excellent step by step instruction of how to do it.  I am sure that everybody, especially the beginners will appreciate the extra time you took to do it.

Offline tinglett

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Re: Pottymill horizontal engine build
« Reply #108 on: March 24, 2015, 01:13:08 AM »
Trepanning the Flywheel

This "trepanning" term is a funny one.  If you look it up the creepy medical definition comes up (ok, nearly everything medical is creepy to me :)), but it also refers to creating a hole by cutting a ring.  I suppose that's what a hole saw does.  It seems like we could use a better term for this since the goal of trepanning the flywheel isn't to create a hole, but rather to create a web for the spokes.

I sliced the flywheel down from 1.125 inch thick to ~0.75 using my bandsaw and then faced it down to 0.75.  This was entertaining and involved clamping a vise to my bandsaw to hold it.  I made partial cuts and rotated it a partial turn once in a while.  It was a long process, but it got done, and left me with a circle of steel that might be useful for something else.  If I didn't have a bandsaw, I would have made a HUGE pile of swarf instead.  Either way works.

My bandsawing was a little sloppy compared to the work from metal supermarkets...so I had to face off quite a bit.  Fortunately I cut far enough out so I had enough material left for the final 0.75 flywheel.  You can see one of my bandsaw cuts had wandered and it was very close to the final thickness.


Now onto trepanning.  I had sliced off the top of the flywheel so the pretty picture I drew by scribing on the mill is no longer attached.  So I painted some layout fluid on the inner and outer parts of the face and scribed a fairly accurate line representing the final flywheel edge (rim and hub sides) as well as another line inland a little as a warning line.

I inserted my test shaft in order to measure the hub.  Simple math for that one.  You can clearly see in this photo that I'm producing a pretty lousy finish when turning the flywheel.  More complaints about that in a bit (apologies in advance :().


I used a cutter to scribe.


Here's the set of markings.  Two inner rings (warning + final) and two outer.


Now started trepanning.  I've only done this on one other flywheel and it didn't go so good.  That was partly because that flywheel was so tiny.  I didn't have excuses here, BUT the first thing I found was the range of my cross slide was horrible with my AXA quick change tool post.  I decided to try my original lantern style post.  Here I'm trying a cutter with a sharp clearance angle that was meant to clear a center.  I thought it might plunge better, but it was producing a bad finish and also wanted to chatter a lot.


This cutter also chattered a bunch.  Blech.


I tried a couple more cutters I had previously ground.  I was getting a rough finish like this when taking off ~5 thousands.  It was frustrating and reminded me of the trouble I had when I was first trying to turn a rod on centers (way back here:  http://www.modelenginemaker.com/index.php?topic=3946.0 )


I tried different angles, and I tried less overhang of the compound under the assumption that the setup isn't rigid enough.  I still got a lousy finish.


BTW, here's a better view of the setup.


Sigh...this will take some experimentation.  But I think I'm doing the right thing by taking the time to figure this out while I have plenty of material to remove.  I'm shooting for .188 deep and I'm still less than one third of the way there.  So I'll keep experimenting.  I'd grind a new cutter, but honestly I don't know what to grind.

I'll also re-check for cutter height.  I think I'm pretty close, but I can test that out more accurately.  I'll also experiment with lathe speed.  I've got quite a change going from the inside to outside on this, but so far I don't think that's it.  I'm producing fairly hot chips (i.e. they are noticeable when they land on me), but they aren't blue.  I also will try some fluid.  I'm cutting dry so far.

Todd

Online sco

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Re: Pottymill horizontal engine build
« Reply #109 on: March 24, 2015, 05:52:05 AM »
Treppanning is never easy - keep at it though and you'll get there!

Simon.
Ars longa, vita brevis.

Offline rodw

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Re: Pottymill horizontal engine build
« Reply #110 on: March 24, 2015, 06:13:43 AM »
Treppanning is never easy - keep at it though and you'll get there
Simon.

X2, Todd I feel your pain. I use insert tooling and tend to use left and right hand facing tooling and open it up with a neutral tool. But on small ones I had to do it on a 20mm OD part the other day and a 4mm slot on a 110mm dia face, I still don't have the right tool for the job. I will say upgrading my lathe made a big difference so I think rigidity plays its part but I guess you don't want to know that!
RodW
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Offline Steamer5

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Re: Pottymill horizontal engine build
« Reply #111 on: March 24, 2015, 08:23:08 AM »
Hi Todd,
 Enjoying the journey with you, your laying out of the flywheel is first class!
When I turned up the wheels for the trolleys, 16 in total, I trepanned both sides of each using a round tipped carbide, 6 mm, I have an Emco 10 lathe so about the same size as yours by the looks, the wheels are about 110mm OD, about the only issue from memory is that the tool fouled when I approached final depth, the tool made a great job of the wheels.

Cheers Kerrin
Get excited and make something!

Online Jo

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Re: Pottymill horizontal engine build
« Reply #112 on: March 24, 2015, 10:03:56 AM »
Hi Todd, I think your grief is being caused by the shape of your tool  :-\

I had a similar job to do recently on my Kitti's flywheel and I ended up using the same tool that I had ground for cutting the inside of the crank case:



This tool is effectively a D bit, so it has the same angle at both the front and rear edges. Because it is made out of a bit of round HSS it does not foul on the bottom on the outer edge.

You could use a tipped boring bar to rough out the bulk, but I must say that I have been feeling more and more inclined toward HSS, it does do an excellent job.

Jo
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Offline Hans

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Re: Pottymill horizontal engine build
« Reply #113 on: March 24, 2015, 01:38:08 PM »
Todd, the layout exercise was very helpful. Thanks for uploading all of the detailed photos.

~Hans

Offline tinglett

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Re: Pottymill horizontal engine build
« Reply #114 on: March 30, 2015, 03:37:23 PM »
Trepanning the Flywheel (part 2)

With the day job getting in the way, progress on this engine has slowed.  I did get a bit of progress done this weekend, mostly consisting of experimenting with various cutters and angles to make trepanning go just a bit better.

I started by grinding a couple new HSS cutters.  I tried making a round one, even though my HSS blanks were rectangular, but it came out pretty good.  I thought this might work well for "dishing out" to get to depth, while I use a traditional straight cutter to square things up.  Note that I used a little layout dye for the HSS.  I had scratched a semi-circle around a bit of drill rod to provide a guide for grinding.  My grinding skills are improving a little.


The round cutter worked ok, but you can see that I got heavy chatter toward the edges.  In theory this was going to work ok.  I'd just make the cut area smaller and smaller.


I continued to "dish" it some, and then went with a straight cutter to square things up.  I still have a long way to go, but thought it best to keep experimenting while I had plenty of material to work with.  I went back to my big quick change tool post as the smaller lantern holder wasn't making it any easier.  Note also that I'm working on the back side of the flywheel with the lathe running in reverse.


I experimented with various ways to present the cutter to fit in the space I had.  Remember this is a 7x12 mini-mill and a 4 inch flywheel.  This first photo shows a setup that was a little dicey.  I wasn't too concerned about losing the cutter as both screws were holding it down, but it needed a heavy angle for clearance and it was too difficult to see.  The following photo shows a more traditional approach, but running on the backside in reverse.   They worked better than before, but range of where I could work was limited by both.



I went back to dishing it out with the round cutter until I was very close to full depth (0.188 which is 3/16").  In the first photo the bowl shape  can be seen along with chattered edges.  Chatter was my enemy in this task, and was also a problem for the straight cutters.  I quickly learned to use chatter as my guide that I was running into the edge and it was time to head back the other direction.  I'd advance using the compound while simultaneously advancing the cross slide.  Passes were, unfortunately, very shallow so this took many passes.


To square it up again I went back to a straight cutter and worked on the back side in reverse.  I'd advance the cutter until it was barely making a cut and then work toward the rim.  As I did this the cutter would effectively be deeper and deeper as I went because it was dished.   Eventually it would chatter so I'd retract the cutter a half turn or so, then continue on.  This gave me a stepped edge as seen in the following photo.  Once I got to the edge, I went back and removed the steps one-half depth at a time for each.  That worked well.


I did the same with the hub, working on the front side this time.  The cutter barely fit there.  But it was all squared up.  As I did this to the rim and hub I measured with calipers.  These dimensions weren't critical, but I wanted the rim to be about 0.313 (5/16") and the hub to be 0.625 (5/8").  I left the rim 10 thousands oversize because I'll be skimming it off later on the mandrel.


A little sandpaper and scotchbrite fixed it up nice.


So of course I get to do it all over again.  I flipped it around, marked the edges of hub and rim again, including warning lines, and got it running true with a DI again.  Note that I had to get a little creative with the compound slide.  This orientation worked so well, I used it for the following cutting steps.  It allowed me to work on the front side of the flywheel which was a little easier to see.


I started dishing again as shown in the following photo.  But now I realized I haven't tried my pointed brazed carbide tools.  I haven't been using these much and they seemed pretty sharp.  I touched it up with a diamond hone and tried it, and to my surprise it not only worked back and forth like the rounded cutter, but it left a fairly decent finish so long as I advanced reasonably slow.  This is shown in the second photo.




So I continued on until I ran out of time last night.  I got to 0.100 depth, so only 0.088 more to go.  You can see the edges are beveling as expected.  It's a little easier to see when the angled cutter is ready to make contact as I advance toward rim or hub.  It will chatter like crazy so as I'm getting deeper I'm not worrying so much about cutting as wide as possible.  When it's a hair from contact, I'll start cranking the cross slide the other way and advance the compound to deepen the depth.


Next time I should have the trepanning done.  All I need to do is get to depth, square up the edges, and sand/scotchbrite it a little.

Todd

Offline b.lindsey

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Re: Pottymill horizontal engine build
« Reply #115 on: March 30, 2015, 04:23:57 PM »
Todd, maybe I missed something. Won't you have to lay out all the holes again now for your spokes? In addition, did you consider using the RT and mill for this rather than trepanning on the lathe?

Bill

Offline MMan

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Re: Pottymill horizontal engine build
« Reply #116 on: March 30, 2015, 05:47:23 PM »
Hi Todd,

You may have got beyond this with your flywheel now but; I had similar problems making the 100mm flywheel on my Bass Stirling - chatter and hassle with the compound. I ended up taking off the compound and making a new base for the QCTP that allowed me to get to larger diameter workpieces and pulled the cutting point back over the saddle, reducing chatter. Here are a couple of pics.

Mman

Offline NickG

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Re: Pottymill horizontal engine build
« Reply #117 on: March 30, 2015, 10:13:16 PM »
I struggled at first until I took a step back and thought about what was happening. As Jo said, This is what your tool needs to look like for the 'trepanning' operation. You need the radius to be smaller than that of the cut out. A normal facing tool with the tool post at the correct angle will allow you to get up to the boss.




Offline tinglett

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Re: Pottymill horizontal engine build
« Reply #118 on: March 31, 2015, 03:48:36 AM »
Thanks for the responses!

Bill...yep, I'll need to mark it again.  The work before was practice, and practice makes perfect :).  I could have cut the spokes and then done the trepanning, but I wasn't so sure about introducing an interrupted cut.  Maybe it would work ok, though, but for now I get to draw it again.  Should be easy this time.

Mman...cool.  I know there are mods to extend the range of the cross slide in a 7x12, but I have my sights set on a slightly larger lathe in my near future.  But if I stick with the 7x12, I need to do something.  I could probably make something offset the full toolpost, too, I suppose.

Nick...I've been getting in there and making sure my tools have clearance, which wasn't true at first.  This was easy to fix when I was grinding the HSS cutters.  I don't think the carbide cutter was rubbing, but it's possible I didn't look.  Still, it was doing a good job and only chattering when the cutter edge hit a deep flat area.   I am curious about your side drawing, though.  Do you think the top rake (is that a top rake?  I should look up the terminology) needs to angle back like that?

I've been trying to get my brain around the difference from turning a diameter vs. turning a face.  Normally I run the cutter perpendicular to the lathe axis when I face off a part, which is why I was trying those crazy orientations to hold the cutter on the side.  But as I was thinking about this I was wondering why it was so.  The rake you have on the top would match the rake I would expect to use when facing so it does make sense.  I will try this when I get back to it later this week.

Offline NickG

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Re: Pottymill horizontal engine build
« Reply #119 on: March 31, 2015, 10:02:21 AM »
Hi there, as a rule of thumb i thought it was supposed to be around 20 degrees top take for HSS cutting steel, 40 ish for aluminium and about 2 for brass or cast iron. True, I suppose the chip is forming the other way facing outwards so maybe a the top of the tool needs to slope more to the left  when looking from the end here. This worked well for me on the last flywheels I did for poppin though as they had quite deep recesses.

 

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