a41capt
Well-Known Member
one with all the accoutrements
Yet Another Webster Begins
- Thread starter CFLBob
- Start date
Help Support Home Model Engine Machinist Forum:
a41capt
Well-Known Member
And one mounted up in the lathe with the cam in place. This one is staged with the cam already case hardened:
Thanks! Very helpful. I was just about to head out to the shop and MIL-TFP figuring if it didn't work, I could just redo the hole on the other side of the center, or on any radius.
(MIL-TFP - an old joke from a made-up MILSPEC. "Make It Like The F*ing Plans" Usually followed with -41C "for once")
Onward to actually cutting this thing. Before that, I'm going to make some landmarks on the blank to cut to.
The process was pretty much as I expected; very manual. I think it's like holding the cam against a grinding wheel, except I think that would turn out smoother and better looking. After spending 3 or 4 hours, I have something that has a cam-like shape, but any outside dimensions that match are purely a coincidence. I'm assuming that this isn't usable.
I know an experienced machinist that I swap emails with now and then, and I told him what I was doing. He asked that since I have a CNC mill, why would I even try to do this? Just clamp it to the table and cut the outline. I did that with the crankshaft counter weight in post 191.
CNC is the strong point in my shop. I need to get better at turning drawings into tool paths.
I will probably try to make one with CNC later today.
I know an experienced machinist that I swap emails with now and then, and I told him what I was doing. He asked that since I have a CNC mill, why would I even try to do this? Just clamp it to the table and cut the outline. I did that with the crankshaft counter weight in post 191.
CNC is the strong point in my shop. I need to get better at turning drawings into tool paths.
I will probably try to make one with CNC later today.
Cogsy
Well-Known Member
How did you go about the cutting? I ask because it looks like there are several different 'lumps' on the cam.
I would have thought the procedure would have gone something like: clamp the blank in the holder and take multiple passes until down to the base circle radius at that one point, then lock the cross-slide at that depth for the rest of the job. Now stop the lathe and rotate the blank by a small amount (probably around 5 degrees) then take a single pass. Now keep indexing around the 5 degrees and taking single passes until you measured nose width is all that is left uncut. This should leave a decent cam with very small facets which should file smooth in a minute or two with a small file (especially under power if you're happy to do it).
Having said all that, for a cam like that I'd use a boring head in reverse on the mill and index it with a rotary table but I think this fixture was likely developed for builders who didn't have access to a mill at all.
I would have thought the procedure would have gone something like: clamp the blank in the holder and take multiple passes until down to the base circle radius at that one point, then lock the cross-slide at that depth for the rest of the job. Now stop the lathe and rotate the blank by a small amount (probably around 5 degrees) then take a single pass. Now keep indexing around the 5 degrees and taking single passes until you measured nose width is all that is left uncut. This should leave a decent cam with very small facets which should file smooth in a minute or two with a small file (especially under power if you're happy to do it).
Having said all that, for a cam like that I'd use a boring head in reverse on the mill and index it with a rotary table but I think this fixture was likely developed for builders who didn't have access to a mill at all.
Hi, Al,
That's what little I got out of the video. I turned the blank more than 5 degree increments, though. Never thought about it, but more like 30 degrees. It never looked like the diagrams in that little screen capture I posted. One problem is that once you've set the cut, I think you've cut the bottom of part. The diagrams show going in one direction, but I thought you had to reverse. The instructions in that video really didn't help me.
The way I look at this is that it was interesting to see how the lathe can be used, but I really didn't know how to use it properly. Each blank takes about 0.3 inches and I started with a foot long bar of 12L14 steel. Right around 40 blanks. I can keep going until I get it right or I can change it over to the mill and shape it under CNC. I have another blank ready to cut.
Take a look at this article. It shows how to form a lobe using the exact method you tried. It works for one lobe or a v8 full of them. All you need to do is figure out how to index the lobe on the fixture a little better and you would have had you a nice part. You already have your fixture made so it's worth another go.
- Joined
- Sep 2, 2011
- Messages
- 1,342
- Reaction score
- 360
bob, the webster doesnt have to have sloped flanks, they can be flat. in my build i have a drawing that shows the cam, you can do it with flat sides so all you need is a rotary table only.
- Joined
- Sep 2, 2011
- Messages
- 1,342
- Reaction score
- 360
heres the link to the post if it helps
https://www.homemodelenginemachinist.com/threads/werowance-builds-a-webster.30772/post-324849
https://www.homemodelenginemachinist.com/threads/werowance-builds-a-webster.30772/post-324849
Thanks, Steve. That really helps. Neat fixture, too, for doing an entire shaft.
47 step of 5 degrees? Sounds like a piece of cake. I know I didn't step anywhere near as fine as that. Probably about 30 degrees because that's like 7 or 8 steps which is more like what I did. I need to draw up a 5 degree angle to put somewhere handy so I can see visualize it on the metal easier.
Yes, it does help. Thanks for that. The part about knowing when to move the rotary table straight was bothering me about Chuck Fellows' method, when I watched his videos. I couldn't figure that out.
I'm leaning toward getting the Upshur method on the lathe to work and if that doesn't work, try CNC on the mill. Since I have it sitting there.
Using the Chuck Fellows method does not require that the rotary table must be moved anywhere. It only rotates. It is hard to get your head around, but it works extremely well and once you have cut a cam using that method , you would never go back to trying to do it on a lathe.
As a general rule of thumb, if there is a cam follower wheel contacting the cam, then the cam can have flat (straight line) flanks. If a tappet rides on the cam, then it needs curved flanks.--Otherwise, if you use a cam with flat flanks it will come around and slap the flat bottom of the tappet, causing the valve to bounce.
As a general rule of thumb, if there is a cam follower wheel contacting the cam, then the cam can have flat (straight line) flanks. If a tappet rides on the cam, then it needs curved flanks.--Otherwise, if you use a cam with flat flanks it will come around and slap the flat bottom of the tappet, causing the valve to bounce.
I've only watched one video by Chuck and only once, so I probably got it wrong. I was pretty sure I saw him moving the mill's table, with the RT on it and thought I recalled him talking about it.
Here is a post I made about using the Chuck Fellows cam making video.
https://www.homemodelenginemachinist.com/threads/quick-way-to-cut-a-cam.26315/
https://www.homemodelenginemachinist.com/threads/quick-way-to-cut-a-cam.26315/
This is the video I watched over the weekend
The only motion of the mill table was setting the depth of cut, as with the video you linked to. I screwed up the first time and didn't grasp it. No idea how, but that's not as important as getting it right now.
The only motion of the mill table was setting the depth of cut, as with the video you linked to. I screwed up the first time and didn't grasp it. No idea how, but that's not as important as getting it right now.
Well, thanks to Steve, @stevehuckss396, the second attempt at turning on the Upshur fixture looks better than the first and is better in every way except one.
The entire bottom half (actually 212 degrees of arc) is supposed to be .094 wide but it's wide by a full 1/32 - .124. My fixture has a half inch diameter washer over the 3/8" hole (filled with a 3/8 rod in the fixture - so it can't move that much. I measured the same way as on the first one. I measure the difference between the blank as I'm turning it down and that half inch washer. It should measure .031 and I thought it did. I didn't see a way to fix this but it might have just occurred to me.
What if I put it back in the fixture with the middle bottom at the closest, cutting point, trim that back until it's the proper thickness, then do my 5 degree counterclockwise turns every 5 degrees until I get to the edge, then turn the blank over on the fixture and go back to the starting point? It approaches the top of the cam from the same direction (CCW) on both sides. I don't see how I could go from one side of the cam all the way around with one fixturing.
The entire bottom half (actually 212 degrees of arc) is supposed to be .094 wide but it's wide by a full 1/32 - .124. My fixture has a half inch diameter washer over the 3/8" hole (filled with a 3/8 rod in the fixture - so it can't move that much. I measured the same way as on the first one. I measure the difference between the blank as I'm turning it down and that half inch washer. It should measure .031 and I thought it did. I didn't see a way to fix this but it might have just occurred to me.
What if I put it back in the fixture with the middle bottom at the closest, cutting point, trim that back until it's the proper thickness, then do my 5 degree counterclockwise turns every 5 degrees until I get to the edge, then turn the blank over on the fixture and go back to the starting point? It approaches the top of the cam from the same direction (CCW) on both sides. I don't see how I could go from one side of the cam all the way around with one fixturing.
Cogsy
Well-Known Member
I can't see why your plan wouldn't work. I also can't see why you couldn't start in the middle like you plan to, cut in one direction (CCW it seems) then reset to the middle and cut in a clockwise direction to finish that side. The fixture should allow you to cut in both directions I think.
Keep in mind that the depth of cut is the lift. Just touch off on the blank and cut what ever the lift is deep. Then rotate and repeat.
I think I have a cam. Well, I'm all but positive I have a cam. Quick summary:
Left to right, first try, then second and third try (on one blank) and today's fourth try.
The first and second are described in the last few posts. The difference between 2 and 3 is that I re-mounted the cam on the fixture and set the depth of cut to get the required wall thickness at the bottom. The problem is the top of the cam. It's easy to see it's too narrow. Instead of 0.254, it's closer to .200.
I think that on one pass midway up the left side, I guess I didn't tighten the SHCS tight enough and the cam slipped getting over cut.
The fourth try was done on my CNC mill. I wrote the G-code by hand. I had fixture with a hole just about perfectly sized for a 1/4-20 screw, so I turned a bushing that press fit into the 3/8 hole and would pass a 1/4-20 screw.
Onward.
Left to right, first try, then second and third try (on one blank) and today's fourth try.
The first and second are described in the last few posts. The difference between 2 and 3 is that I re-mounted the cam on the fixture and set the depth of cut to get the required wall thickness at the bottom. The problem is the top of the cam. It's easy to see it's too narrow. Instead of 0.254, it's closer to .200.
I think that on one pass midway up the left side, I guess I didn't tighten the SHCS tight enough and the cam slipped getting over cut.
The fourth try was done on my CNC mill. I wrote the G-code by hand. I had fixture with a hole just about perfectly sized for a 1/4-20 screw, so I turned a bushing that press fit into the 3/8 hole and would pass a 1/4-20 screw.
Onward.
