Mitering tools and techniques

[WheelNut]

Hey Everybody,

After a five year hiatus from building bikes in my garage I am finally looking to start building some frames again! I'm very excited to get started again, but I'd really like to alleviate on of my major pain points I found with building previously: Tube mitering. I have a junky mill/lathe combo machine (Grizzly G9727) now and I reckon it ought to be able to do some mitering, but what is the best way to jig up a tube for fast, accurate and secure mitering? I have always used a paper template and a file in the past, which has given me good results, but it is so very slow!

A few years ago I had my first shot at tube mitering on this same little mill and it was a mess, but my only tools were a basic machine style vice and a square tubing block. I was having a really hard time getting the mill centered on the tube, and I was also having a hard time getting the tube locked into the vice. I've been looking at the Cobra Miter Daddy and that seems like it could be a good solution as it is quite small and simple. What are some other good solutions?

Are hole saw bits for wood accurate enough? I see lots of people using them. Is there typically hand finishing to do afterwards still?

Thanks in advance for any thoughts and advice!

[Andrew R Stewart]

https://www.flickr.com/photos/731955...7676382588402/ Link to a Flicker stored shot on my set up.

I use a tilting vice, a home made tube holder and a vernier protractor. The tilting vice is a small (3"?) one but can be locked fairly solid at the angle. The tube holder is a length of 2"x1"x0.125" extruded Al box. The tube blocks are Alex Meade's. I have a bunch of fine tooth hole saws on Paragon mandrels. http://www.mo2ls.com/category/SCF.html

I still trial and error the tube to hole saw centering and once centered I do as many of the miters as I can with the same set up. If I'm using a socketed BB shell the BB miters are done freehand, later. I find a need to slightly adjust the miters with a hand file often, so I usually remeasure/mark out the miter to miter dimension after the first is cut and confirmed.

Welcome back to the fold! Andy

[WheelNut]

Thanks for the link Andrew. You are always quick to help!

The tail end of your tube holder is not fixed to that large blue cast iron bit is it? I'm guessing that is just a flat surface block to get your protractor into the right location to take a measurement?

How do you deal with changing your tube size? Do you keep the whole tube holder in the vice and just replace the tube blocks with a different size? Do you re-center the jig to the mill after each tube size switchover?

[Paul Jacobs]

I mitre with my lathe (although I also have a milling machine). The tube is clamped to the cross slide (after removing the top slide) inside a commercially available aluminum tubing block. I have made a spacer, an aluminium cylinder, on which the tubing block sits. This raises the centre of the tube up to the lathe centre. The commercially made tubing blocks are sufficiently accurate for the same spacer to be used with most different diameter tubing blocks and tubes.

The angle of cut is set using a digital protractor on the cross slide with the assistance of a right angle block. The right angle block transfers the angle up to the side of the tube which is a couple of inches above the cross slide.

I strongly recommend the use of carbide tipped hole cutters as shown, particularly with harder tubes like Reynolds 853 or with stainless steel tubes. These last much longer and produce a very clean cut, compared with standard hole saws. N.B. The carbide tipped cutters which I use are designed for cutting thin sheets so there is a collar or depth stop shortly behind the carbide tips. In order to use them as tube cutters this coller has to be removed on the lathe. In the first photo there is a shiny area visible at the back of the cylindrical cutter, which is where the collar was before I removed it with a turning tool.

This photograph shows the aluminum spacer underneath the tubing block. There is a 0.1mm shim on top of the spacer in the photo because I thought I had made it too small but you can see from the cut that the tube is too high not too low. I subsequently removed the shim and all subsequent cuts since for 1", 1 1/8", 1 1/4" and 1 3/8" tubes have been acceptable.

[Andrew R Stewart]

Brad- The underside of the tube holder has a block bolted to it at one end. It's this block that is held in the tilting vice jaws. The tube blocks are also bolted to the holder "box". I drilled a series of holes along the holder and the tube blocks have matching threaded holes so they can be placed along the holder as needed. I have a bunch of Al tube blocks in different sizes but most of the time I have the 1.25" blocks on the holder and use .058" thick walled tubing cut in half to shim down the blocks. This way I don't need to recenter the blocks WRT the mill's spindle. 7 years ago when the photo was taken I used the blue right angle plate as the protractor reference. Now I use a 1,2,3 block on the mill table for that and measure close to the other end of the holder. Andy

[Andrew R Stewart]

Paul- Is that a Myford or Atlas lathe? Many years ago I tried to use my 6" Atlas lather to miter with. But the lathe's flexibility (it was the cast Al version and had PLASTIC gibs in the slides) proved to be a big deal. Now I have a 1940s South Bend 9" A which is vastly more solid. But with the mill I find it quicker as generally little set up is needed. Andy

[Paul Jacobs]

Andy,

It is a long bed, big bore, Myford Super 7 which I bought new and collected directly from the Myford factory in Nottingham shortly before the factory closed in 2011.

It is quite a small lathe (3 1/2" centre height) but quite solid enough for almost everything I want to use it for. It has variable speed control from 26 rpm to 3000 rpm which is useful for tube cutting. It helps with those carbide cutters to run the cutter very fast and advance the tube slowly.

In the UK, a Myford is a good choice because so many were made and are still in use and spares and accessories are widely available. The original factory in Nottingham used to cease production of new lathes on specific dates each year so that they could take in old lathes for regrinding the beds.

Nowadays my Myford is used mainly for making fishing rods. The chuck in the picture below is a small one which I use for fishing rods, it will take much bigger chucks and faceplates.

[WheelNut]

...I have a bunch of Al tube blocks in different sizes but most of the time I have the 1.25" blocks on the holder and use .058" thick walled tubing cut in half to shim down the blocks....

Very clever!

Thanks so much for the feedback guys. This give me some ideas to try. We'll see how it goes.

[Doug Fattic]

Paul, that Myford is a beautiful lathe! I got a nearly unused South Bend 9" tool room lathe when I bought my house. The owner of the house had bought it new before WWII and had barely used it for wood working even though it was a metal lathe. South Bend of course is less than 10 miles away. My wish is that I had the 10" heavy that has a much bigger through hole. However mine came with a nice assortment of accessories.

When I got back from learning in Yorkshire, the 1st tool I wanted was a way machine miter. It is just my nature to want to do something as accurate as possible. It has been a journey to machine miter as well as possible. Several methods I tried had issues until a local engineer designed this one for me. It has some clever features including using a collet system that won't squish the tube out of shape while it is being held (16C or 3J will work). The angle of the arm can be micro changed with a nut on an eye bolt. My goal was to never have to do any touch up with a file after machine mitering. The designer also incorporated a vernier system into angle markings to make precise angle adjustment easier. Of course I appreciate the mechanism that keeps 2 miters in phase with each other.

I'll post pictures in case the concepts of how it is made can be useful.

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[Andrew R Stewart]

Years ago i bought a 3J collet chuck from a still active in part time building guy. I had recently returned from one of Doug's classes and was all pumped up to try to make some tooling as he has. The 3J chuck is really big and some serious machining would be needed to incorporate it into a tubing holder while mitering jig. If anyone is interested in it I'll let it go for far less than I paid:). Andy

[Jamie Medeiros]

Second hand rotary table, scrap metal, v-blocks from Votaw tools, and a self centering vise from Grizzly.

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