Hollow mill ?

[Scott Howard]

I was watching the videos of Ed Falawka and he does a cross rod in one video with what I think they are calling a hollow mill.

This video at the 1 minute.

http://www.youtube.com/watch?v=jS16EEzN-3Q

I have been using a lathe and it takes me a lot longer.

What do I need to look for in buying one of these ? Any tips on using one ? Also what centers it up ? It looks like he just throws it up there and presto . I am sure there is more to it.

Any info would greatly be welcome. I know there are some current and retired machinist who could answer these questions and maybe offer a tip or 2.
Scott

[Bent]

Scott, what Ed calls a hollow end mill is actually an annular cutter. It looks like a regular end mill but is hollow.
Ed does this in two steps. He uses two drill presses. He sets up his cross rods vertically of course, in a jig for this purpose. I suppose he gets it dead straight?
First drill press has a slightly oversized end mill hole with which he starts a bevel on the rod, in order to make it easier for the right size mill to start straight.
Then he does the actual full cut on the second drill press. He applies a liberal amount of grease before the operation.
I wondered to myself: How accurate is this in an ancient-looking drill press with some potential run-out? It does work great for Ed...

I ran this across to my engineer buddy(the one I am getting the milling machine from) He says : We wouldn't do it that way in our shop. There is no guarantee that the hole in the mill is exact dimension, because it is the outside diameter that is accurate in an end mill. He said that he would make the rounds either on a lathe or on a milling machine with a turn table.

With that, expertise has spoken. However, Ed's way works for him; he makes some darn fine fits on those guitars of his.

[burt]

It's a Rotabroach.
It's normally used for cutting holes in girders etc, and is similar to the holesaw that woodworkers use

[Bent]

Thanks Richard, and this proves my buddy's point exactly. We see the "ID taper". We can also envision that as the end of the teeth wear, that ID gets larger in diameter. I'm sure it works fine for aluminum especially It would take a few 1000 crossrods to wear that ID bigger. However, if you do have a lathe or a mill, you know that you'll get it done to the measurement you want.

[Bill Ford]

Much simpler/cheaper...Bill

[Bent]

Bill, that looks like a plug cutter for wood. Some of those cut a slight taper, suitable for a taper plug& tight fit.
I could be mistaken though I think I was mistaken twice before in my life

[Bill Ford]

Bent,
This is a split bushing of sorts (bad picture) Measure across the points of the square cross shaft,drill/bore I.D. so that the sq. shaft is a snug fit, cut a 1/8" slit on the side so that it will clamp the sq. shaft securely in your 3 jaw chuck. the jig/bushing needs to be aprox 3/4" long, with the O.D. large enough for at least a 1/8" wall thickness. another cheep/free part that you can get a more precision bearing surface on the end of the cross shaft. Maybe the drawing will be more clear, if not yell and I will try for a better pic. I had several sizes of these in my toolbox for such an operation.

The black marks on the pic is for approximate jaw position.

Bill

[Scott Howard]

I will get a picture of what I use this weekend . I wish I had seen this before I bought what I have been using.

I have most , if not all of the rods turned for my next project so I am in no hurry to do anything right now .

But this is some good info here. This is the type of stuff I need . Simple solutions !!!!
I think I have seen that type of bushing / drawing before , maybe on the other forum ?
My memory is not the best.

[Bent]

Thanks for the sketch and extra explanation, Bill. When I finally got my eyes un-crossed and took my welding glasses off I could indeed see that it is what you say and not some imagined plug cutter DUH!

I just marvel at all the great ideas emanating from the minds of like-thinking individuals. We have Eldon with his truck-tire valve-stem-string-roller, to all your nifty inventions. I mean, the next step will be a book by one of you guys entitled Steel Guitar Building for Dummies.

What a neat little group we are becoming

[Scott Howard]

Here is what I have been using. It was a collet that when I bought it I thought it would just screw into the lathe. I ended up having to cut the back of it off for some reason, but don't remember why. I have one for 3/8 and 5/16 and the square stock fit pretty snug in them . I just chuck it in the lathe and tighten the hose clamp. I have had good results with it but I am not good with the lathe and was looking for a easier way of doing it.

I guess I need to learn more about using the lathe and spend some shop time with it.