Making a custom lathe bit on the cheap --

[goodfellow]

I need to turn a groove in an old Brit brake drum. It has a pocket in the end and a straight boring bar won't do. So I made this custom bit in just under an hour. I always keep some 1/2" square hot rolled mild steel bar (from Home Depot) on hand just for making lathe cutting bits. It's much cheaper and they work better than the brazed stuff you get from China. My lathe Quick change tool post has a 1/2" max capacity; hence I use 1/2" square stock.

They're easy to make, and save a lot of money because individual inserts can be purchased very cheaply on ebay. I was lucky enough a few years ago and bought an entire lot of 500 inserts (of varying sizes and shapes) for just a few $$ on ebay.

Here is the process:

Cut to length and machine the ends square. Then for this type of triangular insert I mark the bar and machine a 5-7 degree relief angle. It's necessary for these inserts because they don't have a manufactured relief angle, but that's also good because all six sides of the insert can be used for cutting.









Now offset in the vise for 7 degrees and machine a pocket for the insert (also provide some undercut for the lower edge so it won't contact a tight work piece.



Once that's finished I setup the piece on its side and measure for a 30 degree angle. Then I flip it and machine the opposite side





This is the result: A nice 60 degree insert pocket



Use a punch to center the insert and mark for a 5/32 hole





Drill the hole and run the bit through a wire wheel to de-burr the edges. Then attach the insert with a small machine screw.





Now it's just a matter of heating the body with a torch to red hot, and bend the desired length and angle of the offset. --- Done and ready to do some work. These things are cheap and easy to make -- and for small jobs and smaller lathes they work very well.

[muddy]

Nice work Ray! Is this what you made your gear for the lathe with?

Sent from my E6910 using Tapatalk

[goodfellow]

Nice work Ray! Is this what you made your gear for the lathe with?

Sent from my E6910 using Tapatalk

No Tim, that gear was needed to for my lathe to be able to cut an 18TPI pitch on that Sears compressed air moisture trap/filter fitting that I machined. This cutter is needed to get around a hub boss and cut a recessed groove.