How to drill square holes

[FLOPGUY]

I need to drill a series of square holes in a brass.
I am building a tracker like what you would see in  player piano. I need to drill about fifty 1/8" holes about 1/8" apart. This will be done into a 1" solid brass rod.

Any ideas how to do this?

Thanks
Mike

[Lew_Merrick_PE]

Mike -- You need to make a broach.  For .125 (inch) square holes, you can use a .125 square lathe tool or piece of tool steel (silver steel to our friends on the other side of the pond).  First (assuming pre-hardened lathe tool bit), you grind a slip-fit ø.125 diameter on the end of the bit to act as a "lead" for your broach.  Then you carefully stone the (4) corners as if they were going to be used (axially) as a shaper bit (i.e. hook them to a nice sharp edge).  Then mount the bit in a sleeve that will fit an arbor press (I usually just drill a slightly smaller hole and press it in).  You can now drill your ø.125 holes and then broach them to square.

Depending on the thickness you need to broach, you may need to do it in several steps to clear the chips.  Commercially made broaches have several (progressively larger) teeth on them so you can get through the entire thickness in one shove.  This is something (especially in a small size such as .125) that is hard to do in the home shop environment (i.e. without a really good universal grinder).

You might want to search for a RotoBroach to see another way to approach this.  I suspect that a RotoBroach would not work for you without a good deal more tooling in the application you describe.

Does this help?

[FLOPGUY]

Yea, actually that does help alot.

I dont have the capability to make a broach, but do see on the internet, a company that sells the correct size broach... that sonds like the direction I will need to go..

Thanks
Mike

[Lew_Merrick_PE]

Mike -- Not knowing what you need to accomplish with your broaching makes it hard to be specific, but many (if not most) small jobs can be done with a home-shop made broach.  A 1/8'th inch toolbit and a little bit of sneakiness can, in most cases, do the job.  I will readily agree that a well made commercial broach will (almost always) be superior to a home-made broach.  However, that is usually driven by cost, performance, and quantity issues -- and I know nothing of your parameters there.

Good luck -- and let us know how it turns out.

[BillTodd]

Do they really need to be square all the way through?  Can you drill the rear of the hole slightly larger so you only have to broach a couple of mm. 

If not can you fabricate the piece i.e. mill a series of slots in one half and cover with a the other half. A tight lapped joint will be almost invisible.

Bill

[Chazz]

I know it's ot in most budgets, but do a u-tube search for 'rotary broaches', pretty slick stuff (with price to match).

Cheers,
Chazz

[Fergus OMore]

There a Brit who writes on such things as well as intersting improvements to his lathe.

Try homepages.mcb.net/howe/

Again, my favourite workshop book is  G H Thomas's Model Engineers Workshop Manual has quite a bit on your problem