Pottymill horizontal engine build

[tinglett]

Cutting the Spokes (part 1)

I've slowed quite a bit, but got a good start on the spokes of the flywheel today.  I finished trepanning the second side finding that cutters shown by Nick really do work well.  I ground a rake on the top, but it was only about 10 degrees and it seemed to help.  I'd still get some chatter at the edges, but it wasn't too bad.  I made nice shoulders on the hub and rim as before.

Next I mounted it to the mandrel I made earlier and trued up the outer rim.  This was just a few thousandths to clean up and I hit it with some scotchbrite for good measure.



Here's how it looks on the engine.  It seems to be a good scale for it.  I had to chuck it in my mill vise for the photo.  I suppose I'd better start thinking about how I'm going to mount it.


I centered the RT and then centered the flywheel like this.   Interesting enough, it was still a bit off.   I used a DTI to finish getting it absolutely centered.  However, I'm only making spokes so it would have been ok as-is, but it was good practice for me.



Next I scratched out the inner and outer radii for the spoke holes as well as lines representing the centerlines of the spoke.  I thought these would keep me oriented and signal mistakes.


My angles were easy.  With 5 spokes, 360 degrees / 5 spokes = 72 degrees/spoke.  My RT moves 4 degrees per turn of the dial, so that's 18 turns from spoke to spoke.  The inner holes are centered between the spokes at 36 degrees, which is an easy full 9 turns.  The XY table was locked as I drilled these, and I would set one of the locks on the RT each time I turned to hold things steady.


Drilling turns out difficult because my mill is Z challenged.  The center drill shown above was no problem, but this was to be a 3/8 inch hole and the bits were far too long.   I happened to have a set of numbered screw machine drills, so I used the biggest I had, #1, followed by a 3/8 2-flute (drilling) end mill.  They worked great and gave me lots of room.  It's possible the end mill would have drilled fine all by itself, but I went through the sequence for each hole.



Then repeat for 4 more holes.  18 more cranks on the RT to position each, and lock the table.





After the center holes were drilled, 9 more cranks got me back to zero on the RT.  Next I cranked two turns for an 8 degree offset for the outer holes.  I had to crank out X on the XY table to get at this radius.  I re-locked the XY.  These holes were 3/16 inch so my regular drills worked fine.


After each hole, crank 18 for the corresponding hole on the next spoke.  Note that this means I was skipping the other holes.  That second pass is coming up.  I did this when I did a trial run a few posts ago and I'm convinced it's a good idea.  When it's always 18 cranks, it's hard to mess up.  Here are all five holes drilled.


Now I had to advance 14 cranks to get to the "odd" holes.  I could have gone backward, but it's less work thinking about backlash by moving always forward.  The spoke line was nice here because I could see the new hole was landing in the right place.


Then it was a matter of advancing 18 cranks per spoke and drilling the next 4 outer holes.   Here it is all drilled.


After this was done, Twenty more cranks (2+18) would advance me back to zero.


Hmm...but now I see a new problem.  I need to cut out these webs with a mill, and my clamping is going to get in the way.  I'll start by replacing those bolts with short ones, but that might not be enough.  I may need some lower profile clamps of some kind.  Always something.

Thanks for checking in.

Todd

[NickG]

Nice work, the engine is looking good. I need to try cutting a flywheel with spokes from the solid now I've got a rotary table. I think they often look better that some of the grotty castings I've tried.

[tinglett]

Cutting the Spokes (part 2)

In my last post I drilled all the holes that are the "corners" of the cutouts that form the spokes.  Tonight I decided to cut the arcs on the outer edge of these openings.  If this isn't clear, the photos will show what I'm up to.

I decided to cut these in at least two passes.  In the end I took four passes until I was satisfied.  With the RT and flywheel centered under the mill head, I cranked out the X table until I was at the outer radius.  My outer holes were 3/16 inch and it so happens this is my smallest end mill so there wasn't extra math to calculate the end mill's outer edge.  In order to do multiple passes, I cranked out X so it came up about 12 thousands short of the full radius.  Also, when I cut the arc I started 4 degrees into the opening (i.e. one extra crank) and I stopped short 4 degrees.  So instead of 14 total cranks for the arc, I used only 12 while roughing it open.   I took 3-4 passes to get to depth.  Anything deeper seemed to be too much for my mini-mill.

I started with a 4-flute end-mill because it was longer and I had clamps to clear, but by the second slot I decided to try the 2-flute and found it fit in the space (barely).  Here's the setup where I started with the 4-flute.  Maybe you can see I'm slightly inland and I know it's clear I'm a few degrees into the cutout.


I took a shallow cut as my first pass.  This is the first time I've rotated the RT while milling so I wasn't sure how stable it was going to be.  It was pretty smooth.  I took the opportunity to plunge on both ends during this pass.  I think this was a good idea for the later cuts because I could hear when I was at the end of the cut as I moved into the pre-cut opening.


This photo from above makes it pretty clear how I shifted the cut inland.  The working theory was that I'd make these cuts all around, and then make a light finishing pass at the full radius and length of cut.


As I switched to my 2-flute for the second cut, I also remembered to set my Z depth stop.  This was a very good idea because I would no longer need to worry about trashing my RT.  I'd also use the visible distance of mill head to stop to eyeball my depth adjustment when making the 3 passes.  I also used locks when I could.  My XY locks were always on, and I would lock the RT whenever I was plunging.  And I'd use the Z lock whenever I was cutting while rotating the RT.


I went around making the five cuts for the five spoke cutouts.


So far so good.  Looks a little rough.  Now time to clean up.


I went around at the finishing radius which was an easy 10 thousandths to remove.  But note the bit of gouging that still remained.  Maybe I should have reserved 20 thousandths.


The outer radius for the spokes isn't that critical provided I don't change the start/end angles.  So I took another 5 thousandths.  It wasn't good enough, but another 5 thousandths got me into the ballpark.  It's looking pretty clean.


And that's about it for today.  It occurs to me that I haven't backed up the camera to show the whole setup in a while, so here it is in case there's something I forgot to say about it.  Sometimes a picture is worth a thousand words as they say.


Thanks again for checking in.  This weekend I'm hoping to finish off the spokes.  The next cuts are the "tricky" ones that require I shift the XY and turn to an angle to cut between the inner and outer holes.  That ought to be interesting.

Todd

[NickG]

Looking good Todd, there is quite a lot of working stuff out isn't there. Did you cut at full depth for the finishing passes on the outer rad and did you go both ways or avoid climb milling?

[tinglett]

Nick,

Yeah, for the finishing cuts I did them at full depth in a normal (not climb) cut.  I guess I didn't think too much about direction.  I assume a climb cut might pull on the RT a bit.  But the regular cut was in the right direction for "going forward" with my RT.     I was only taking 5 thousandths so it was a pretty easy cut.  I just dropped the head down onto the Z stop I set earlier and went for it.  The cutting was rather fast even though I went around for two passes.

I'm hoping there won't be too much cleanup to do when the spokes are all cut.  We'll see.

Todd

[tinglett]

Cutting the Spokes (part 3)

I got a little shop time in this evening ahead of the weekend.  I wasn't able to accomplish everything to finish the spokes, so there will be one more installment, but I made good progress.

Recall I had the holes drilled and the outer arcs cut by the end of the last installment.  Now I will cut the radius that runs tangent from the inner hole to the outer hole.  Today I got one of these for each spoke cut.  All 5 spokes cut at the same general settings so it's less fidgeting to do them in steps going round and round the rotary table than it is to finish each spoke with lots of cranking of dials.

For my spoke configuration the software says I need an offset of 0.220 inches and a rotation of 4.61 degrees.  My RT uses degrees/minutes/seconds so this is 4 degrees, 36 minutes, 36 seconds.  I'll round that to 40 seconds which is what my table rotary can do.   Unfortunately these blasted settings are both backwards on the dials.  That means figuring out where the dials should land, rotating them further than that setting, and rotating back to hit the setting exactly going in the right direction.  I always go clockwise for this so I don't forget.

Now the offset of 0.220 does not compensate for the radius of the cutter I am going to use.  But I first dialed in 0.220 anyway so I can use my little scratch tool to verify I got the settings right.  Here it is...and looks pretty good.


I dialed the Y to adjust 3/32 inch for the 3/16 diameter end mill I'm using.  I went an extra 20 thousandths so I can make cleanup passes after doing the slot cuts.  Still looking good!  The finished cut looks like it might be approximately 20 thousandths offset.  Good.



Now I need to rotate the RT 18 turns (72 degrees) to get to the next spoke position.  That's going to be error prone because I won't be stopping at 0 degrees on the dial anymore.  So if there's any real good ideas in this build log, it might be this one.  I figured I'll for certain screw this up, so I added blue tape like this to the top of the dial.  I drew a line off the end of a square, and then I slit the tape with a razor blade so I could spin the dial again.  It's painter's tape so easy to remove when I'm done.  I put it on top of the dial so it's easier to see.


Ok, well now it's repeat, repeat, repeat, until all 5 spokes are done.  All I needed to do was dial 18 cranks and use the blue tape as my target position for the 18th crank.



I should mention that I wasn't really watching the X dial that much as I cranked.  It was easy to visually see the start and end of the path I was cutting so I wasn't too concerned about this.  The main thing was that I didn't want to do was gouge into the outer arc, so I'd start by plunging at the outer edge with the mill off in order to get the starting position right, and then I'd mill toward the middle.  I used 3-4 passes as before to cut all the way through.


Two more to go and the hard part's done.



Now was time to finish the edge.  I have 20 thousandths to go and decided to finish in two passes.   All I had to do was crank the table around, 18 cranks per spoke, and run off 10 thousandths.  I'd machine from the outer hole to the inner and back so I'd get a normal cut then a finishing climb cut.  The climb cut wasn't so important, but this got the mill back to a starting point for the next spoke (after I'd rotate to it, of course).


Here I got concerned.  That line didn't quite look like it was going to line up.  Sure enough, I realized I got the RT dial wrong.  Pppffft.   These markings on the RT's dial are going to take practice.   I think next time if I need to back up the dial I will back up a whole extra turn (i.e. -4 degrees) and then move forward to take the excess off.   That is, I'll calculate this forward setting and dial it in.  I'm finding it very hard to run the vernier on this RT...but learning to do it backward as well as forward seems crazy at the moment.   One thing I can do is eyeball the setting between the minutes and decide if it makes sense.  Getting the right minutes is probably "good enough" for this angle (better than 2 hundredths a degree).


Now they were looking better.  It's too bad there's a shadow here, but the spoke at 8 o'clock is looking pretty good.  Same with the one at 10 o'clock.  The other's only show the ratty cut on the inside that's going to be tossed.


Finally, since I was going to call it enough for the night, I reset the Y offset, double checked it was still centered with a rod in the hole, and installed my marking rod to double check that I returned the RT properly back to zero.


Tomorrow I'll do this all again on the other side of the spoke.  I'm a little concerned about this one because the waste material is going to fall.  I don't want the end mill to bind up when that happens.  Not sure what I can really do about that, but I'm thinking it may help if I finish the cut at the large (inner) hole end so there is more space when it plops.

Todd

[tinglett]

By the way, hopefully *most* people see the photos in my previous post properly.  I find when I rotate photos in photobucket, it takes a long time for external uses of the photos to come up proper.  Very annoying.  I suppose I should learn to rotate the photos properly before uploading to photobucket, but you'd think they could get that right.

Next build log I'll try something different.  Meanwhile, I'll suffer with photobucket and hopefully you guys won't need to rotate your heads too much to see what I'm talking about.

Todd

[rodw]

By the way, hopefully *most* people see the photos in my previous post properly.  I find when I rotate photos in photobucket, it takes a long time for external uses of the photos to come up proper.  Very annoying.  I suppose I should learn to rotate the photos properly before uploading to photobucket, but you'd think they could get that right.

Next build log I'll try something different.  Meanwhile, I'll suffer with photobucket and hopefully you guys won't need to rotate your heads too much to see what I'm talking about.

Todd

Windows photo viewer lets you rotate photos before you upload. The other free photo tool I've used for years is Irfanview. It has  a batch mode so I use it to downsample all my photos in a LoRes folder under the folder I store the photos in. Then I upload those photos to Photobucket.

These days I use Adobe Lightroom which is awesome and there is a Photobucket plugin available for about $3.00 so it can upload straight to Photobucket. (but I still create my copies in a LoRes folder like I did for years with Irfanview.)

[Jo]

Tomorrow I'll do this all again on the other side of the spoke.  I'm a little concerned about this one because the waste material is going to fall.  I don't want the end mill to bind up when that happens.  Not sure what I can really do about that, but I'm thinking it may help if I finish the cut at the large (inner) hole end so there is more space when it plops.

Hi Todd, What I expect you will find is that as the last little bit is being milled the cutter pressure will push the waste material away from the cutting edge, add to that the fact that the waste will bend down due to its weight and it should all be ok 

I bet you will be please to get over the wind, wind, wind of the mill handles. Any blisters? 

Jo

[tinglett]

Cutting the Spokes (part 3) and Finishing the Flywheel

It's the weekend and shop time.  Well, I got time on Sunday anyway and was able to finish off the flywheel.  It isn't completely done as it needs a little cleanup and polish as well as a way to secure it to the shaft (setscrew?).  But it's looking like a flywheel now!

Last time I had the arc and one side of each cutout finished.  Today was time for the other side.

Recall the software said the angle should be 4.61 degrees and offset 220 thousandths in the Y axis.  I'm going to the other end of the spoke, so this will be 72 degrees (the spoke angle) + 4.61 = 76.61 degrees which is 72 deg, 36 min, 36 sec.  I cranked it to that angle and updated my blue tape to the new position so I can find this angle again and again as I finish each spoke.  I offset Y by exactly 220 thou so I could use my little scratch tool as a sanity check.  Here it is after scratching from the outer hole to the inner hole.  Looks like the correct position.


I dialed Y an extra 20 thousandths so I could make finishing passes after cutting out the spokes.  I cut each using 4 passes, finishing in the larger inside hole.   As Jo pointed out, the pie wedge would angle away from the cutter until the left outer part would touch the spoke, but by then it would fall down harmlessly.  Nice.



Now I would do 18 cranks (72 degrees for my 5-spoke flywheel) to get to the next spoke and repeat.



I did the first finishing cut by removing 15 thousands (of the 20).  I'd start at the inside hole where there was more clearance, work to the outside until you could hear it enter the outside hole, and then would return back to the inside hole to be ready for the next spoke.


Here I had dialed to the exact measurement for the final cut.  It was clearly a bit off.


With a little experimenting, I ended up taking off an extra 7 thousandths.  You can still see a little shade change where the hole meets the spoke, but it's very hard to feel.  I suspect the holes are slightly oversize.  But these are just spokes, so at this point I was only making adjustments to make the sanding and polishing work easier.


This is about all I can do on the mill with RT.


It matches the diagram.  Well, of course it does .  Here you can see all the numbers I was working from as a reference.


And here it is on the engine.


I'll need to trim the shaft to length and do something to secure the flywheel to it.  I'm thinking a setscrew would be nice, but not exactly sure how to drill in such a tight spot.  I could thread and/or loctite.  While I'm thinking about that, I may turn the engine around and work on the eccentric and valve linkage for a while.

Todd

[b.lindsey]

Nicely done Todd, I always enjoy seeing updates on this engine.

Bill

[John Rudd]

Nice bit of machining there....as for securing it to the shaft, you could use a taper style fastening or just drill/tap a grub screw fixing by drilling at an angle.....

[rodw]

It's really interesting to follow your progress. I'm sure others will have other ideas but I wonder if you could drill and tap for a setscrew on an angle? Hold the flywheel on a mandrel held in a collet block. If the sesetscrew was on the inside, it would hardly be noticed. Looks like John beat me to it while typing!

[Don1966]

A real nice job and save on your flywheel Todd. 

Don

[NickG]

Much prefer your flywheel to my casting from RDG. Lot of
Work in it mind you. Have you thought about running around the spoke edges with a 45 dog angles cutter? I haven't got one but have seen used to good effect - tried with a csk bit to put chamfered edges on but that didn't really work!