Thread: Advice on putting together a bit of jig-tooling

Click for large view - Uploaded with Skitch

This bit is part of a jig for mitering bicycle tubing. The two round sides simulate different diameter tubing. These faces are used to lock against a fishmouth'd end of the tube being mitered. The centerline of each "tube" is .563" from the centerline of the block.

What's the problem? The diameters are 1-5/16" and 1-7/16". Instead, I need a block that simulates 31.8mm and 32.4mm.

The original block, pictured above, was made using two form cutters. Well, I don't have 31.8mm and 32.4mm form cutters and it's not worth buying them. So I decided to make the new block out of three pieces, two partial cylinders and a block in the middle.

Click for large view - Uploaded with Skitch

I made the two cylinders and then sliced off most of one side of each. Next step is to machine a block which I can mount the two semi-cylinders against.

Click for large view - Uploaded with Skitch

That's the theoretical blueprint. But I have practical concerns.... How do I setup things so that I can ensure I've got my cylinders dead-square aligned with the block? It will stink if the cylinder is pushed to the right or left of the centerline.

I thought about machining a channel dead square along the centerline of the block which the cylinder could set into. Then I clamp it together, drill, and pin it?

Anyway, this is my first attempt at making accurate tooling, so I am sure you folks have better tricks to to assemble this thing. I haven't machined the center block yet. I have a lathe, vertical mill, and simple setup pieces to use. (mill vise, parallels, edge-finders)

Regards

Welcome to tool making. The way a lot of tools are made is exactly as you have proposed, a bunch to pieces that are made and then assembled into a compete tool. For what you want to do, fasten the pieces together say with cap screws, check the alignment of the pieces, and when everything is exactly where you want it, dowel the pieces together. The cap screws hold it together, the dowels keep the pieces aligned. Just keep in mind that if you want to disassembly the tool, there will have to be a way of removing the dowels.
Tom

Don't forget liberal use of your .0005 or better indicator.

I would mill a groove in the center of the flat side of the two cylindrical pieces. Them mill corresponding tongues on the center section. No need for dowels.

Gene

Originally Posted by easymike299

I would mill a groove in the center of the flat side of the two cylindrical pieces. Them mill corresponding tongues on the center section. No need for dowels.

Gene

I liked your idea Gene. Tomorrow I'll make the female grooves.

Click for large view - Uploaded with Skitch

Originally Posted by karavshin

I liked your idea Gene. Tomorrow I'll make the female grooves.

Click for large view - Uploaded with Skitch

"I liked your idea Gene. Tomorrow I'll make the female grooves."

The female grooves should probably have a "Honeymoon Fit" for better accuracy.

Regards,

Stan-

karavshin

Would like to see the finished product.

Gene

Jig: guides a cutter

Fixture: holds workpiece in location

A clear vocabulary is the sign of a clear mind.

Originally Posted by easymike299

karavshin

Would like to see the finished product.

Gene

Finished it up tonight.

Click for large view - Uploaded with Skitch

Click for large view - Uploaded with Skitch

Click for large view - Uploaded with Skitch


I'm very happy with my result. This is the first real bit of accurate tooling I've ever made.

There are some cosmetic errors. You can see the live-center hole on the end of the semi-cylinder for instance. And I started out (like a moron) trying to drill the 3/4" main hole w/ a twist drill. Gnawed the metal. Then I realized that the extremely sharp 4-fluted HSS 3/4" end mill would do a considerably nicer job.

The only dimensional error I made was that one arm of the center block was 18.74mm instead of 19.05. Fortunately a thin shim fixed that issue so i can bolt the semi-cylinders on just fine. The frustrating thing is that I cannot figure out where in my milling procedure I introduced the error.

But overall, the dimensioning was good. All the key lengths are correct to around 0.05mm and I think the centering of the pieces along the central axis worked well.

So......... it feels like an accomplishment. Now I can get back to finishing the bicycle frame after a fifteen hour detour.