Crazy linear bearing idea!

[mvaughn]

Hi all,

I was down at my local Home Depot the other night and I couldn't help but check out their wall mounted panel cutter.

The circular saw was mounted on a sled and used bearings like the drawings below. I thought they were pretty slick but I question their capability for precision.

They consist of u-bolts, black washers (they looked like plastic of some sort), and what looked identical to a nylon anti-scuff pad that you press into furniture legs.

This may have been discussed before, but I failed to find any mention.

Oh, BTW, please excuse my limited drawing skills. I just threw this together in 2 minutes.

What are your opinions?

[JavaDog]

Yeah, I would imagine accuracy takes a back-seat on that design.

[ynneb]

A variation could be some skate bearing threaded onto the u-bolt with washers packing them for spacing. If you used 2 bearings on the U-bolt and somehow put a beaing instead of the nylon pin, you could tighten the U-bolt down until all 3 bearings came into contact with the rod. That may increase the accuracy / hold a bit.

[JavaDog]

Originally Posted by ynneb A variation could be some skate bearing threaded onto the u-bolt with washers packing them for spacing. If you used 2 bearings on the U-bolt and somehow put a beaing instead of the nylon pin, you could tighten the U-bolt down until all 3 bearings came into contact with the rod. That may increase the accuracy / hold a bit.

Ooo...now there is a cool idea.

[ynneb]

This is the sort of thing I was thinking.

Sorry for posting this pic in two sections, but it seemed to apply to both discussions.

[dsadams]

I could see how this might work for short runs but, as it is a closed loop design, you couldn't go past a support on the rail.

[macmiester]

This thread has got me thinking about other alternate designs... I have some I-beam and was thinking this might work as a design for linear bearings. I call it the big ball rail. I'd use 2 big ball bearings on both sides of the I-beam that have been drilled and set with bearings. I would set these in square tube that would fit over the rail. Here's a pic of what I'm thinking... My goal here is to have mininmal contact surface and that would not be prone to getting buggered up with debris. Any thoughts? Has anyone tried something like this?

[mvaughn]

I like the big ball rail idea. (kinda sounds funny, lol)

I would suggest that you bevel the inner edges of the I-beam to increas the contact points for the ball bearings.


How would you drill an exactly centered hold in the ball bearings?

[macmiester]

I have 2 ideas to drill the bearing. Since I don't own a mill, but have a press, I would drill a hole in a clamped piece of aluminium stock the slightly smaller than the ball, take the ball out of the freezer and drop it in the hole, give the vise a little extra snug and re-chuck a bit for the shaft hole. The other idea is to take the balls to the machine shop here at work and have them chuck it on their rotary table

[macmiester]

I just talked to a machinist... It seems that ball bearings are hard than the tools to drill em... Hmm. But I'm still not quite convinced as the ball I'm planning to use is from a mouse as they are just rubber coated steel balls. I'm betting they aren't hardened though and could be drilled. Any thoughts?

[flybynight]

Hi, I do construction/cabinet work and have used panel saws and have toyed with the idea of building one for home shop, so I've done some research before. The rings you see on the U-bolts are "delrin" rings. It can be purchased as a hollow tube with different diameters and wall thicknesses. Most machine supply houses carry it. Hope this hepls a bit. Thanks

[40fordcoupe]

I recently saw this same basic idea used on a blacksmiths treadle hammer. The rail was heavy four inch square tubing. There were two skate wheels mounted of the stationery fixture on each side about one foot apart making eight wheels in all. The tubing became the upper part of the hammer and travel was about one foot in the Z axis. The bearings were mounted on eccentric bolts and were adjusted so each wheel was lightly compressed and the hammer stroke was straight with light friction but without noticable wobble. The total weight of the hammer was probably about thirty pounds.

Also given the amount of punishment they take skateboard wheels might work out well too.