Posted by: gregory ® 07/27/2007, 15:10:18 Author Profile eMail author Edit

I am designing a machine that uses 4 horizontal pivot arms (2" X 2" and bearing load is axially and radially). I am wondering how the bearing arrangement should be (spacers, washers, housing design,clamping, etc...). Center payload (floating)is 500lbs approx. Pivot hinges are fixed to side bodies (not shown). Arms swing 90 degrees only. I've narrowed my search to a Double-Row Angular Contact Bearing. Any information is greatly appreciated. Thank you.

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Re: pivot arm design (bearings)
Re: pivot arm design (bearings) -- gregory	Post Reply	Top of thread	Forum

Posted by: jboggs ® 07/31/2007, 08:14:21 Author Profile eMail author Edit

I agree with what seems to be the consensus opinion here that plane bushings are the way to go here rather than rolling-element bearings. I've had very good success with composite bearings such as the DU, DX, or other products from GGB (www.garlockbearings.com/). They take very high loads, can handle small misalignments, and are generally weather resistant, and easy to install. (No - I'm not on their payroll!) Modified by Administrator at Tue, Jul 31, 2007, 18:09:31

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Re: pivot arm design (bearings)
Re: pivot arm design (bearings) -- gregory	Post Reply	Top of thread	Forum

Posted by: Kelly Bramble ® 07/28/2007, 08:20:33 Author Profile eMail author Edit

Nice picture (we don't allways get this). My first thought while looking at the mechanism is to use Spherical type bearings at the pivot locations. Since nothing is built perfect, Spherical typ bearing would help with alignment. How dependable cycles do you need for the mechanism?

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Re: Re: pivot arm design (bearings)
Re: Re: pivot arm design (bearings) -- Kelly Bramble	Post Reply	Top of thread	Forum

Posted by: randykimball ® 07/29/2007, 00:51:56 Author Profile eMail author Edit

..back from vacation... I agree it depends on the cycles you expect. I have a set of machines in production working well very similar to this design... VERY SIMILAR.. the pivoting links deflect punch cutters during punch cycles... I used 4140HT (50 RC) with shoulder screws and no bearings.. ..even to my amazement they have run for many thousands of cycles with no signs of probmatic wear.... (sorry...I can't quote the actual number of cycles because of a failure in the cycle reporting system). However if you need meta-cycles with no wear I'd go with needle bearings for the pivot load and needle thrust bearings for the axial loads. Or .... aluminum bronze for thrust. The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, never let suggestions go unsaid nor fail to listen to them.

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Re: Re: Re: pivot arm design (bearings)
Re: Re: Re: pivot arm design (bearings) -- randykimball	Post Reply	Top of thread	Forum

Posted by: gregory ® 07/30/2007, 11:06:26 Author Profile eMail author Edit

Thanks for the input. It's good to know real working situations such as the punch. I forgot to mention that the components will be machined from billet aluminum. Space is VERY limited on the design. I should also let you know that the machine is a lifting device for handicapped persons (airliner terminal to airliner seat). These arms make the machine "wide" when transporting the person, so the cycle is very low for this application. It needs to be robust because it is carrying a human.

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Re: Re: Re: Re: pivot arm design (bearings)
Re: Re: Re: Re: pivot arm design (bearings) -- gregory	Post Reply	Top of thread	Forum

Posted by: devitg ® 07/30/2007, 15:12:13 Author Profile eMail author Edit

Why not bushings , hardened steel pins. as speed is low and cycles not so much

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Re: Re: Re: Re: Re: pivot arm design (bearings)
Re: Re: Re: Re: Re: pivot arm design (bearings) -- devitg	Post Reply	Top of thread	Forum

Posted by: gregory ® 07/30/2007, 17:54:04 Author Profile eMail author Edit

Bushing may be the way to go. I'm not an expert in bearings and bushings, but I do know they are cheaper, and there's less maintenance involved. One question...what about the load on the end of the bushings? (axial). Wouldn't you need thrust bearings? I chose the double row angular contact bearings because they take both axial and radial loads, but in a smaller bearing design. Here's a picture of what I have so far.

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Re: pivot arm design (bearings)
Re: Re: Re: Re: Re: Re: pivot arm design (bearings) -- gregory	Post Reply	Top of thread	Forum

Posted by: randykimball ® 07/30/2007, 23:25:52 Author Profile eMail author Edit

I'd suggest custom made UHMW (Ultra High Mocular Weight polyetholene) bushings with heads on them to act as the thrust. This material has no manintenace requirements, has excellent wear, will handle the loads, machines like a dream, and installs easily. The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, never let suggestions go unsaid nor fail to listen to them. Modified by randykimball at Mon, Jul 30, 2007, 23:28:26

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pivot arm design (bearings)
Re: Re: Re: Re: Re: Re: pivot arm design (bearings) -- gregory	Post Reply	Top of thread	Forum

Posted by: devitg ® 07/30/2007, 19:11:11 Author Profile eMail author Edit

For this kind of work , bush is the most suited device , for trust load use a plain bush , like a washer , and some bush have shoulders , so in only one part you have all features . that kind of bearing have no seal , to avoid water and dust , bushes does not need it , also you can use some kind of plastic for bushing. Can you state what are the loads.??

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Re: pivot arm design (bearings)
Re: pivot arm design (bearings) -- devitg	Post Reply	Top of thread	Forum

Posted by: gregory ® 07/31/2007, 13:18:58 Author Profile eMail author Edit

I took everyone's suggestions and came up with a plan. I decided to use the "bushing and washers" (both UHMW) design instead of the "bushing with shoulders" design, because the pivot arm is horizontal. With the shoulder design I had no way of keeping the bushing centered in the pivot arm, when the load is applied (maybe retainer clips... but that needs more room, somthing I'm short on at the moment). One question...should the bushing be a press fit or slip fit?

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Re: Re: pivot arm design (bearings)
Re: Re: pivot arm design (bearings) -- gregory	Post Reply	Top of thread	Forum

Posted by: jboggs ® 07/31/2007, 16:21:21 Author Profile eMail author Edit

After looking at your layout I have a couple of thoughts. One - Maximize the distance between the upper and lower bearings as much as possible. The greater their separation, the lower their individual moment loads. Two - I don't know if you intended your sketch to be to scale or not, but if it is, the wall of the bushing looks very thick, too thick. The bushings I am familiar with carry a very high load with very thin walls. And they are press-fit, which eliminates the concern about slippage.

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Re: Re: pivot arm design (bearings)
Re: Re: pivot arm design (bearings) -- gregory	Post Reply	Top of thread	Forum

Posted by: devitg ® 07/31/2007, 14:00:49 Author Profile eMail author Edit

You can use two bushing , with shoulders so you do not need any retain device , and let a small space free at the middle. I would prefer to press fit it , and then machine or ream the hole to best suit the pin , or you can locate it by a small elastic pin located radial to the bush.

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Re: Re: pivot arm design (bearings)
Re: Re: pivot arm design (bearings) -- gregory	Post Reply	Top of thread	Forum

Posted by: randykimball ® 07/31/2007, 13:58:29 Author Profile eMail author Edit

With UHMW make them a snug slip fit/light press... drop the .005" clearance. In reality some heads (washers) will be a little snug and some will have something near your .005" of slack... this should be no problem. What I meant to say, was, use two bushings with heads... one from each side. This takes care of center, and controls the thrust "washer" position, plus (something that counts at production) reduces the parts count. ..... (devitg) you owe me a coke, we posted the two bushing comments at the same time. The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, never let suggestions go unsaid nor fail to listen to them. Modified by randykimball at Tue, Jul 31, 2007, 14:08:46

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Re: Re: Re: pivot arm design (bearings)
Re: Re: Re: pivot arm design (bearings) -- randykimball	Post Reply	Top of thread	Forum

Posted by: CCR5600Design ® 07/31/2007, 15:01:31 Author Profile eMail author Edit

This arrangement looks very similar to a kingpin design used on straight axle trucks. Good durability at a low price. Great ideas, guys! Ron "What we need are more people who specialize in the impossible." - Theodore Roethke Modified by CCR5600Design at Tue, Jul 31, 2007, 15:56:16

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Re: Re: Re: Re: pivot arm design (bearings)
Re: Re: Re: Re: pivot arm design (bearings) -- CCR5600Design	Post Reply	Top of thread	Forum

Posted by: gregory ® 07/31/2007, 17:07:11 Author Profile eMail author Edit

I understand what you guys are talking about. I'm excited because this seems easy to manufacture, and most of all...CHEAPER. RandyKimball, you quoted saying: "With UHMW make them a snug slip fit/light press... drop the .005" clearance. In reality some heads (washers) will be a little snug and some will have something near your .005" of slack... this should be no problem." ...do you mean no slack at all? I'd prefer that. This is one of my concerns: I don't want the center "sagging" (shown in green) because of the pivot joints. I like the idea of the two bushings (with washer incorporated), pressed from both ends. I'll change the bushing wall thickness too. Great info guys! Thanks.

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Re: Re: Re: Re: Re: pivot arm design (bearings)
Re: Re: Re: Re: Re: pivot arm design (bearings) -- gregory	Post Reply	Top of thread	Forum

Posted by: randykimball ® 07/31/2007, 17:48:22 Author Profile eMail author Edit

Sure, with UHMW you can make them snug as you like. Just have a taper lead in on the pin. Have radius edges on the slots so the thrusts can be pushed in. ...Remember the wider the joint the less sag you will develop. The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, never let suggestions go unsaid nor fail to listen to them.

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