T-slot cutters

[Ian S C]

Tel mentions odd numbered teeth, also it is a good idea not to accurately index the spacing, that will dampen out vibration, and it will improve the cut.     Ian SC

[Don1966]

That came out nice Hugh, did the cutter hold up very well or did you have to sharpen it again?  I have a casting i need to cut T slots in also.

Don

[ths]

Well the first cutter performed beautifully on the little rotary table, and would appear to be able to go several more rounds without resharpening. I ran it at about 600rpm, which according to the Tubal Cain book is below recommended speed. On none of the four slots did it feel much above body temperature.

The speed was dropped to 300rpm for the second cutter, which is 5/8" diameter. It only had 1 slot to cut, and it appeared to do it as well as the first. This was in the foot casting of the GHT quick action hand rest. I did a lot of his designs when I was doing a foundry course some years ago. Don't be fooled by the appearance of the slot in the end of the casting. Even a cursory look at the cutter will show that it's turned itself into a dovetail cutter of an unknown angle. No prizes for guessing the angle.



I'm wondering firstly, if there was a hard section in the casting that the cutter could not deal with, the dovetailing begins about an inch down the slot. I'm tending to discount this theory, as I don't see why a hard spot would be in the centre of the casting surrounded by lovely soft cast iron. The endmill that made the slot had no trouble at all.

Which leaves the cutter, and I'm wondering if, despite the good soaking it got in the oven, it was not of a consistent hardness. Well, I'll make another cutter and try again. If the casting proves truculent, I have another to play with.

Cheers, Hugh.

[steamer]

It could have been an inclusion....perhaps sand.

Dave

[MuellerNick]

I ran it at about 600rpm, which according to the Tubal Cain book is below recommended speed.

If the diameter was 12.7 mm, cutting speed then was 24 m/min. That's OK for HSS and for a T-slot cutter (they should run slower than an endmill).


There are three different schools how to cut a T-slot:
1.) pre-cut the slot, so the TSC will have to cut full height. I'm not with that!
2.) pre-cut to full depth, so the TSC won't have something to bite in the middle.
3.) Pre-cut, so the TSC has 1/2 to 1/3 of his height to cut in the slot part.


I prefer the last, it runs smoother and the chips still get out quite good and chip volume still is reduced compared to method 1. Method 2 is a bit harder to the cutter.


I'd use a cutting speed of say 15 m/min (makes about 380 RPM for ø12.7).


HTH,
Nick

[steamer]

Good Point Nick!

 

Dave