Thomson Super 8 Linear Bushing question?

[widgitmaster]

I have purchaced eight of these Thomson Super 8 Linear Bushings from Enco, along with some .500 dia x 12" long case hardened linear shafting. I have been building a pair of "Mini Routers", a little at a time from scraps and scrounges. The X-axis has all the weight, and the furthest distance from the spindle; consequently, this axis has the most trouble with endplay in the slide bearings. The endplay is magnified by the distance to the spindle, and makes it feel even worse!

So I purchaced the round linear ball bushings in an attempt to rectify this problem. Now, my question is what size bore does the outer diameter of the bushing require? I have searched everewhare, and have found no such information!

The diameter of the shaft is .49925"
The outer diameter of the bushing is 7/8" approximately.

The bottom view of my mini router will be modified to eliminate the two rectangular bars with the delrin block in the middle, and replaced with one large solid block with a pair of linear bushings for each rail. Then the center of the block will be hogged out to accept the delrin nut.

I would like to use snap rings to keep the bushings in place, and that would suggest a slight slip fit for the bushings! To avoid boring the holes oversized, I would like a formula or such to calculate the fit for the specified shaft diameter. Otherwise I will be boring test blocks untill I get the right size!

Thanks,
Eric

[ViperTX]

Check out the Thomson Industries web site.

[widgitmaster]

Originally Posted by ViperTX Check out the Thomson Industries web site.

I think I found it!

http://www.danahermotion.com/file_br...cument_id=3695

Thomson Industries was sold to Danher Motion........

It looks like the recomended bore size is .8750-.8755" diameter with a shaft of .4995-.5000 diameter.

Eric

[Ken_Shea]

You gotta love the internet !

[mjarus]

will be modified to eliminate the two rectangular bars with the delrin block in the middle

I assume that you are talking about a delrin slide for the rails here. If so, how is that mounted in the aluminum blocks? The aluminum blocks look solid from the underside. Is it hogged out on top? If so, can you post a pic when you get it off? I am curious to see the current set up.

Also, why are you going to use your delrin nut? I thought you had a new brass a/b nut you were working on.

BTW, I purchased some of your delrin nuts and so far with preliminary messing around with them they seem pretty darn good! I was going to use 2 per screw to combat backlash, but I don't think that will be necessary.

Oh yeah, also is the current delrin block on the screw threaded the whole way through? How long is it? Do you use a tap to cut the threads or do you use a single point tool on the lathe?

mjarus.

[widgitmaster]

Originally Posted by mjarus I assume that you are talking about a delrin slide for the rails here. If so, how is that mounted in the aluminum blocks? The aluminum blocks look solid from the underside. Is it hogged out on top? If so, can you post a pic when you get it off? I am curious to see the current set up. Also, why are you going to use your delrin nut? I thought you had a new brass a/b nut you were working on. BTW, I purchased some of your delrin nuts and so far with preliminary messing around with them they seem pretty darn good! I was going to use 2 per screw to combat backlash, but I don't think that will be necessary. Oh yeah, also is the current delrin block on the screw threaded the whole way through? How long is it? Do you use a tap to cut the threads or do you use a single point tool on the lathe? mjarus.

MJARUS,
The bronze nut is a completely different project!
I used a tap to make the Acme threads!

This "Mini-Router" project has been on going for many months, everything was tight and smooth sliding except the X-Axis, so I ordered some closed linear ball bushings to try to tighten it up! The bushings did not come with any information, so I had to do some research to figure out what bore diameter was required. Then I made a large solid block and bored two close tollerance holes straight through it, and the bushings went in really precice!

I had to do a little calculation to get the specific number for the bore, as the bearing documentation was based on a .50000" diameter rail; consequently, my rails are .49925, so I shrunk the bore accordingly!

The exsisting slide was made from two pieces of aluminum, with a delrin nut, and teflon bushings. They were sliding nicely, but the teflon was too soft and the bore elongated! So The Ball bushing assembly is much better now!

Next, I have to make an internal square groove cutting tool to put in the boring head, so that I can cut a groove for an expanding spring ring. That will keep the ball bushings from sliding out! Then I will make a little plastic spacer that will go between the two ball bushings.

In order to make the groove tool, I have to order a 1/4" x 7" grinding wheel for my surface grinder. The wheels I have are too coarce and too wide!

While I'm waiting for the grinding wheels, I will drill & tap the end holes, and hog out the middle of the aluminum block to hold the delrin nut!

Eric

[ger21]

I used super 12 bearings on my wood router. I noticed with a slightly loose fit, you can adjust the tightness of the bearings on the shafts by shimming the bearing in the hole with a piece of paper, or wrapping it with tape.

But, during assembly, I found that shimming them tighter wasn't necessary, due to slight misalignment of my whole assembly. The slight play made it self aligning, with what appears to be no play at all.

[mjarus]

That is some nice work Eric. Thanks for the replies and the pictures. Was the 10-1/2 tap very expensive? Just curious, as I said, I already got the delrin nuts from you, so I don't particularly need one, but I would imagine a decent tap that large was not cheap.

What do you plan on machining on that particular machine? It looks pretty solid. I am only going to do PCBs with the one I am building so I have to keep telling myself not to over-engineer.

mjarus.

[widgitmaster]

Thanks Mjarus!

I believe the taps were around $47 ea, I have two, one for plastic and the other for metals.

Actually this "Mini-Router" started out as a prototype to see if I could build an inexpensive production unit, using the basic materials at my fingertips! However, it has become much more than I planned, and I hope it will motivate people to throw their money at it!

I have been designing a simple spindle with a 1/4" maximum collet, it should be able to run at 30,000 RPM with no trouble, providing I can find some nice bearings for it!

The spindle will have a 1/4" shaft on the drive end, and a flange with 4 #10-32 threaded holes for mounting a motor plate.

The body of the spindle slides in a clamp mounting bracket, designed for the "Mini-Router". But this spindle will be adaptable to most any DIY router, giving the designer a break from the flimbsy Dremel tools!

If this works, I'll have a local shop mas-produce some of the components on their CNC machines!

There does not seem to be much of a choice for spindles, other than big and bulky wood routers, and laminate trimmers!

My AutoCAD skills are limited to wire type drawings, as solids were not taught back in the early 80's when I took classes! I'm so busy making stuff in my new shop, I don't have time to teach myself the solid CAM stuff!

[mjarus]

I have been wondering what to do about the spindle... I am just delaying the inevitable decision that must be made. You are absolutely right though, there are no real good options out there unless you want to spend some big bucks. For me this is a hobby, so that doesn't really appeal to me. I will be interested in seeing what you come up with! The only "real" option I was considering thus far was just buying a spindle from Sherline, there was another post somewhere on here about that and it seemed to make some sense.

mjarus.

[Jason Ross]

The super 8 is an adjustable, self aligning bearing. Check out the spb 8 adj on the danahermotion web site. By duplicating the slot to adjust the tolerance of the hole you can increase the preload. With extreme caution you can make the hole slightly undersized or the shaft slightly oversized (by about .0001~.0002") and you can achieve a preload. You want to use good aluminum (t6) or the bearing plates will Brinell the housing and you will develop play over time.