Request for help reducing friction & rolling noise of a cam follower roller.

Hi everyone,
I would like to ask if anyone could please help me with the following
problem.
I have a small conjugate dual-roller rib or blade cam that has an
inner and outer cam-follower roller working on a corresponding inner
and outer cam curve. The cam curve is basically a curved "rib" with a
roller on each side of the rib. The rollers oscillate about a swing
arm in response to cam oscillation.
The force of the small 3/16" OD rollers is pinching the cam rib and
causing drag on the manually oscillated cam. The system also has
roller noise that must be reduced as much as possible. The system is
very sensitive to any friction between the cam & roller, or any drag
or noise in the system.
I've tried to polish the cam, and add lube, but there is still too
much friction. I could also try to polish the rollers.
Is there any type of hard coating I can apply to the cam and/or
rollers that will help significantly ? Any type of special lube I
could use ?
The maximum Hertz contact stress is probably around 180,000 PSI. Right
now, the cam is made from hardened 4140 and the roller is hardened A2
Tool Steel.
Is there any type of non-metallic roller that I could use ?
I would appreciate any suggestions for alternate materials, coatings,
lubes, or anything else I might try.
Thanks for your help.
John
Reply to
John2005
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The stress seems high for little rollers (I presume rolling on plain shafts?) How much better to use two bigger ball bearing races in a bigger side cam. Can you make space?
Brian Whatcott Altus OK
Reply to
Brian Whatcott
Hi Brian,
Thanks for your message.
One of the big problems on the design is the space constraint. The cam has to be so small that I need to use a small diameter cam follower roller in order to keep from undercutting the cam. The points on the cam near the dwells get too sharp with a larger diameter roller. It seemed even going to a 1/4" OD roller produced interference, but perhaps I could cheat a little. It does not look possible to use a larger roller than 1/4" OD and I would rather stay with a 3/16" OD roller so I can use the same cam and not redesign the curve for a 1/4" OD roller.
Presently, I'm making the rollers from 3/16" OD A2 drill rod. I cut the roller to length, drill a 2 mm hole in it, and then press a 2 mm OD hardened dowel through the on-center hole. The dowel extends from each end of the roller & the dowel "rotates with" the roller as it oscillates. The ends of the dowel are supported by plastic busings made by
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As the roller oscillates, the dowel pin / shaft oscillates in the plastic bushings. It's a basic yoke type of roller mount.
Perhaps the plastic bushings are giving a little & I would be better off just letting the ends of the 2 mm OD dowel oscillate in the 4140 yoke, & lube it with some grease. It may be possible there is some deflection of the shaft causing problems, or perhaps heat treating the roller made it a little egg shaped. I did not think there would be any significant friction at these rollers, but I think the load is so high for such a small roller that this is causing the problem. The two rollers are pinching the cam rib, and causing drag. Springs return the cam to it's home position & drag is preventing this. Stronger springs mean more physical effort from the user. I need some way to reduce friction at the rollers as much as possible. Reducing the friction should also reduce the noise problem.
Other than this friction problem, the design works fine, which makes it frustrating the get everything together and run into an unforeseen problem like this.
Timken makes a 1/4" OD drawn cup needle roller. Perhaps I could install this over a 1/8" dowel and give that a try. The possible problem I see here is that drawn cup needle rollers rely on a press fit to properly size them, and make them truly round. It may also fit loose on the shaft unless I make a custom shaft.
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makes a miniature stud type cam follower (Part # CFS 2.5 V) with a 5 mm diameter ( 0.197" OD) which should be close enough. It can handle a 220 pound static load, the only problem is that the last time I checked, they cost about $50.00 a piece and the product requires two rollers per unit. I think it will be cost prohibitive.
It seems a rolling element bearing is the best way to reduce friction, drag, & noise as much as possible, along with applying lube to the roller OD & making sure the surfaces are smooth. The problem is finding a bearing that has a diameter of 3/16" and that can carry a static load of 90 to 130 pounds.
A non-metallic self lubricating roller also seems appealing, but it's a matter of finding something that small that can handle the load.
Any other feedback would be appreciated.
Thanks again, John
Reply to
John2005
..
This Timken approach seems so much better than the present arrangement, it can hardly fail.....
Brian Whatcott Altus OK
Reply to
Brian Whatcott
Hi Brian,
Perhaps I could use an oversized 1/8" OD dowel as the shaft for the Timken drawn cup bearing. As long as the bearing is round enough it might work OK. Drawn cup bearings rely on a press fit to size the ID and to make them truly round and not egg shaped. In this application, there will be no press fit as the bearing will just spin on a shaft and the cam curve will be in contact with the bearings hardened outer shell or drawn cup.
The cam curve is designed for a 3/16" OD roller. Do you think I can cheat a little and use the 1/4" OD roller with my existing cams or will I most likely need to design and make new cams for the 1/4" OD roller ? Perhaps it's worth a shot to use the larger roller with the existing cams.
Thanks again, John
Reply to
John2005
They also rely on the housing to support the cup so it doesn't distort under load. A 1/8 x 1/4 bearing has 1/16" between the shaft and the OD of the cup. If 2/3 of that is the diameter of the needles, then the cup wall is only about .020". Without a housing to support it, the cup is going transfer the load thru only a small number of needles. Now your max stress is a result of a significant fraction of the load carried by the contact between the 1/8" shaft and a single .040" needle.
Ned Simmons
Reply to
Ned Simmons
I'd think the displacement with rotation would be different from what you want, but it would give you quick insight into noise and friction factors....
Brian W
Reply to
Brian Whatcott
Good point Ned, the drawn cup wall is very thin.
Going to a full complement bearing filled all the way around with rollers would seem to help support the thin cup under the roller load ? This seems much better than a caged bearing with spaces between the rollers. Do you think I would still likely have cup distortion problems with a full complement drawn cup needle bearing ? At only . 020" thick, I guess distortion would take place in either case and at a roller load of 90 to 130 pounds, would probably be significant enough to cause rolling problems.
I may have to break down and buy the IKO stud cam followers at $50.00 each. At least I can get it working best as possible and worry about final unit cost later. I would think the stud type miniature cam follower has a thicker outer ring wall, but I have not checked it yet. It has adequate load rating so I guess that's all that matters since it's designed as a cam-follower. Using the IKO cam-followers and adding lube between the cam and roller would seem to get the roller friction as low as possible. I just have to check for stud tear-out because I won't have much metal around the cam-follower stud, so I could run into problems there as well.
It's very close to where it needs to be, but If I can significantly reduce roller friction, it looks like it would really work well.
Thanks John
Reply to
John2005
Hello John, May I suggest the following link:
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and check out the page
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, your answer might reside there, check out the first paragraph mentioning a test on timken hardness bearings, if it impressed Mitsubishi maybe it will impress you too by contributing to your system. Dyno Tests for this lubricant was just done last week, where do you live, what state? maybe I can help you ? Christian Petaluma
Reply to
BambooFibers
After checking into this further, I think that this might be a case where the cam curves are not accurate enough and the cam is kind of binding between the two rollers. Can anyone please tell me what the tolerance of the cam curves should be, relative to the cam rotation axis, for a conjugate dual roller cam as shown in FIG. 2 at the following link ? ...
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The cam was made from 4140 steel, CNC machined, and then the curve was flame induction hardened. I probably should have had the cam hardened and then ground to high accuracy.
Thanks John
Reply to
John2005
Regarding figure 2 at the link in my previous post, the very inner curve is not present in my cam. My cam just has the curved "rib" or blade that is in-between the two rollers.
Reply to
John2005
Should have said "flame or induction hardened", I don't really know which, I think they said flame hardened once then induction hardened another time. I don't know as I did not specify the hardening technique, I just specified that the parts should be hardened to 50-55 RC. I expected the tolerances to be held in any case, or to be told by someone if the tolerances could not be held due to heat treat distortion or some other factor.
Reply to
John2005

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