Good Evening Eveyone
Well - I have been making another tool myself (because this time you can't even buy it in this size)
A Square broach.
I hade the inspiration from the video that was uploaded on youtube by Chris (Clickspring):
https://www.youtube.com/watch?v=MYI1slVGziUI however chose a different approach on making it. I didn't have any square tool steel and picked a 3mm round bar i had around.
The broach shall finally produce 1.6mm square holes!
I started with machining the square form of the teeth. The tooth pitch is 2,5mm and i machined 2mm wide slots into the bar. The Idea is that I can move the bar out of the collet tooth by tooth and each "flange" still supports the unfinished broach when machining the teeth.
If you look at the support of the bar - that is just a square brass piece with a reamed hole in it. Then put into a small vice and clamped down on the table at the right position. Works pretty good when you do not have a dividing head tailstock!
The next step was executed on the lathe. I first pull out the workpiece (the grooving tool works as an end stop so I pull it out exactly the amount required). Then I machine the groove.
After that, I change the tool and machine the clearance angle on the back of each tooth. I chose 4° (that is how the top slide of the lathe is adjusted). Every tooth has 0.04mm more diameter than the one before. That gives 0.02mm depth of cut per tooth (since the depth of cut is in the radius)
Picture no. 5 shows how the unfinished broach looks when you take it out of the lathe, with the two last "flanges" left.
After finishing on the lathe, I hardened the broach using a reducing flame (in order not to get too much scale) and sharpened it on a fine honing stone.
And of course I also tested it (the picture is a little blurry
):
It works great. The hole on the left has been drilled slightly too big, the one on the right seemed to be quite right.
I will definitely make other size broaches (2mm, 2.5mm, 3mm or so) - I could have used them several times before!