[jakk100]

What type of linear bearing do you use?
(The kind that is used with a continuously supported round shaft.)
Ball bearing?
Frelon?
Ceramic coated?
Cheap sources?
Your thoughts are surely appreciated.
Thanks
Jakk

[resotek]

I hope someone will take the time to respond to Jakk. From the pictures I've seen on here it seems like roller blade bearings are popular on X and Y. What about Z? I can't tell what folks are using in this regard.

Cheers,
Mel

[cncadmin]

I'd use any high quailty SS Ball bearing. The Z i'd use a linear slide.

[jakk100]

The kind of bearing I would like advise on is for continuously supported precision shaft.
My choice is a linear bearing using ball bearings-see photo.
Product literature suggests the frelon linear bearings offer more vibration damping (good) but higher coefficient of friction (.125-.200), and may mask alignment issues….may wear faster???
The linear ball bearings offer lower .002-.004 coefficient of friction (good), but I am concerned they may vibrate on the shaft.??? Or am I all wet. The cost is comparable from what I’ve seen.
So with that said… I think the linear ball bearing would be the way to go.
What are your thoughts and experiences?
Frelon or ball bearing?
Thanks
Jakk

[HuFlungDung]

Hi Jak100

(hey, there's a pun there ;0 )

You'd want to be using fully hardened shaft in those linear ball bearings, if that is a consideration. All those tiny points of ball contact do not actually amount to a "good bearing" at all, even though the friction may be low, and providing you have such an exacting fit that they are practically preloaded.

Plastic is a bit draggy as you pointed out.

I'd use Oilite bushings, running on Chrome plated shafting, although it may be a trick to fasten the bushings into an opensided housing. However, working through the open side of the bearing housing, I think a guy could countersink a flathead screw into the bushing to retain it from the inside.

I would also maximize the length (through design) between bearings running on any one rail to minimize slew and jamming.

[balsaman]

I am thinking the ball bearings would be fine on regular shafting (3/4" cold rolled even?). Yes the balls don't make a ton of contact with the shaft, but there are lots of them, and the pressure isn't that high on a home made machine. It would last many years IMHO. Even with low friction the bearing will be quite tight, ie. no play at all. remember the balls just need to roll along. They actually roll thru the bearing and out the back into a tunnel built in to bring it back around to the front. They work slick (punn intended).

I would stay away from the plastic bearings.

Eric

[HuFlungDung]

Cold rolled shafting is pretty soft.

I'm not sure how you would calculate the area of contact of balls with a shaft, but no matter how many you have, the area of contact is still near zero. This automatically creates high pressure contact and the hard balls will very quickly roll a groove into the soft material. This creates unwanted play.

A true raceway needs to be contoured to fit the ball.

I'd be interested to know if these linear bearings are packed with an undersize ball every other ball. This would improve ball flow and reduce skidding of one ball locking against the other because of simultaneous contact with the inner and outer raceway and the ball in front of it.

[balsaman]

Hi,

Good point about the contact area being close to zero. I don't think the balls differ in size. On my linear bearings, (which are the blocks that run on the squarish rails) the balls are all the same size.

Eric

[Zephrant]

Hu- Many of the raceways now have plastic carriers that isolate the balls from each other, eliminating the need for over/under sizing of every other ball.
(Or so their literature says...)

Zeph

[HuFlungDung]

Oh, thanks, Zeph, that should be good for the bearing performance.

[DieGuy]

Are these claims true? Seems Frelon is a good bearing material.

An expanded series of 148 Frelon lined linear bearings from Quality Bearings & Components can tolerate upto 1,500 psi over the portion of the bearing that is carrying the load. These Frelon lined anodized aluminium bearings carry 4 to 8 times the load of ball bearings. A 1/2" I.D. Frelon bearing will carry as much load as a 1" I.D. ball bearing. Long service life for these self-lubricated bearings is another major benefit. Although wear rates are affected by surface finish, shaft hardness. length of travel, contamination and lubrication, these bearings last on average 4 to 8 times longer than ball bearings.

http://www.qbcbearings.com/New/Frelon.htm

[mxtras]

I now prefer to use mainly linear bearings such as THK HRS series. The cost might be a bit higher than other methods but you get what you pay for.

I recently completed a 1350 pound, 63" wide motion system capable of positioning accuracies of less than 1 micron (0.00004", 0.001MM) - for this application, medium preload THK bearings were used to eliminate stick-slip.

I have also used Turcite (sheet material, bonded) for high loads with mixed results.

Moglice (specialized, low shrink epoxy) is an absolutely awesome method, but offers a bit of stick-slip which may create difficulty for extremely precise, small moves. It is far superior for dovetail or box ways where you have the potential for metal to metal contact during initial moves due to the displacement of the way lube. If you ever re-furbish a Bridgeport machine, I would definitely urge you to look into the benefits of this type of material for way construction/repair/alignment - and it is not that expensive or difficult to use.

Using rollers on cold rolled material or the round bearings (Thompson) mentioned in a previous post would be adequate for certain applications, but I have had problems with both of these methods. I previously designed a composite processing machine which used the Thompson type (round) bearings to guide a shuttle over 30' at relatively slow speeds and the rails began to exhibit signs of wear after only 8 months of use - with an automatic lubricator and dynamic loads that were less than 1/5 of the maximum recommendations. I was a bit disappointed. The second machine of similar design used THK HSR type bearing blocks (I think they were NSK or another brand) - more initial cost, but provided much longer life - and less noise....and no warranty replacement costs, so they were actually less costly in the long run. Granted this was a production machine not a hobby machine but the lesson is there.

I would venture to say that the selection depends on your goals and your budget. Each method of guiding has its place and its advantages. Each method has disadvantages of course - sometimes it is only cost, sometimes the design dictates a specific method. The selection of guiding components primarily depends on speeds, forces, accuracy requirements and budget constraints.

Guiding is no place to skimp when sitting down to design a machine in my opinion.

Keep this going - let’s hear from everyone!

[mxtras]

Come on - anybody else?

Scott

[DareBee]

I also have had experience (bad) of trying to use CR TGP shaft with linear BALL bearings. It was a fairly heavy load (not exceeding bearing capacity though) and I couldn't even get I stroke out of it.
The bearing balls just dug into the shaft and it was scrap (had a row of large grooves down the length).
The system probably would have worked for awhile with Oilite's or Frelon bearings due to there improved weight distribution.

[Halfnutz]

What is "Cr TGP" ?

[mxtras]

I am pretty sure it stands for Cold Rolled, Tempered, Ground and Polished.

Nice material - but it has been my dreadful, expensive experience that it is not compatible with ball bushings/bearings unless the loads and speeds are rediculously slow - even then I would suggest a different method or a hardened and chromed shaft.

Scott

[Halfnutz]

Wow, I had no idea. I just figured all the shiny stuff was , well, shiny. And shiny is good right? I geusse not, necessarily. But seriously, I did know Thompson's real specific about what to use, and suggests not deviating. I wonder what the cheap, well, cheaper anyway, knock off rails are. So the main difference is polished vs chromed and hardened. Thats what I love about this site. So much knoweledge.

[mxtras]

Turned, Ground and Polished - not Tempered. - sorry guys! I gave the material TOO much credit!

The rails made by Thompson are case hardened, ground and chromed - yes. Carbide tooling can drill them, contrary to popular opinion. Been there.

The typical "TGP" material may be shiny, but it's not hardened. It's either 1018 or 1048 steel in a normalized condition which is about 18-20C hardness. In comparison, Thompson's shafts are 60C surface hardness. The case hardened shafts from McMaster can be as high as 65C(Rockwell C scale)...not too bad in my book.

I don't know what diameter you guys use, but you may investigate these links if you haven't seen them before -

http://www.smi4motion.com/shafting.htm
http://www.metalsdepot.com/products/...dround&LimAcc=

Scott

[DareBee]

Good research Mxtras was about to give a correction untill I read on. ;-)
IMO TGP is very reasonably priced for precision shafting - as long as soft suits your application.

damn - Paul you getting anywhere with adding a spell checker here

[mxtras]

I am not knocking the TGP material - not at all. It has it's place. Just passing along info, opinion and relavant experience if any. I agree that it is reasonably priced!

I vote for the spell checker, too!! or better yet - how about speech to text instead?

Scott