This one takes a bit of time but it's worth it. Brazed ceramic inserts are too expensive, while honing HSS takes too long when doing roughing and general machinig work. Here's a way for you to buy cheap TNMA inserts from e-bay and never have to worry about cutting tool costs again.
I'll try to show how to make a 60 degree straight roughing cutter, and in a follow-on thread also make an offset RH cutter
I started with the following items:
1) 3ft. 1/2" square steel bar from Tractor Supply -- $6.00
2) TNMA-333 inserts bought bulk on ebay -- got 100 of them for less that 25 cents each
3) Some 5mm hardware for mockup
First i cut some 4" blanks from the steel bar and machined the ends square
Next take an insert and use a carbide scribe to marke the outline of the pocket
These TNMA inserts don't have a rake to them (that's good). The second letter "N" indicates "no rake" and that means that these inserts will have a total of six
useable cutting edges. However, for accurate cutting, a rake (or offset) is needed; hence I'll have to machine a rake angle into the holder. This isn't "rocket science", any rake angle from 4-8 degreees should be ok!
I opted for a 5 degree rake since it's easiest to read on an angle finder.
Here it's positioned in the viise
Mill the depth to the approximate thickness of the insert --
Use a loose insert to check fit --
Once it's machined to size, run the bit thought a wire wheel on the bench grinder to deburr it, and it should look like this --
Mark the insert for a screw hole with a center punch (use the insert itself as a template), and clamp the holder in the drill press vise at a 5 degree offset (so it will sit square) to drill a hole.
Do a little hand fitting with a file to make sure the insert fits tight.
Now mark the sides of the holder with the carbide scribe and mill both sides to 30 degrees
Here is the finished product --
Please note that I used this cheap nut and bolt for mock-up only. I will get a proper grade 8 capscrew this week. I used a nut to secure this insert because I have found that even if I tap these holders, eventually they will come loose and the threads will strip. With this method, I can just replace the capscrew and nut when they get worn from stress.
Here is our new holder compared to a brazed bit -- ours is stronger, lasts longer, costs pennies and will last forever.
Next thread -- a RH bit holder. Enjoy!!!!!!