End Mill Extension

**nova_robotics** · Jan 3, 2023, 02:49 AM

I got a problem. Turns out my tool isn't quite long enough. I didn't think my CNC machine would end up agreeing with my ex-girlfriends.

**metric_taper** · Jan 3, 2023, 08:25 PM

I did something similar this weekend with a 1/4-28 tap. I was helping my neighbor remove a broken glow plug from a V6 diesel engine.
Warning, what ever you do, DO NOT BREAK THEM OFF.
It turned into 3 days of work. I was making different size drill guides that would thread into the M8x1.0 glow plug threads, those were cleared out of the head with a kit he bought from Amazon for this purpose. That kit has a step drill that is 7mm at the large end, that drills out what's left of the 8mm threaded portion. Problem was it was drilled cockeyed. and left a burr on the extension tube below those threads in an aluminum head. The idea is that step drill's smaller diameter puts in the correct hole size for a 1/4x28 tap. So it's tapped, then a puller that threads into that is screwed in, and in this case it's a jack screw type puller. So no feel of what's going on. It stripped out and did not remove the remains of the glow plug. So much more work going deeper into what was left.

This photo has the new glow plug, and the remains of the one pulled out.

End Mill Extension-img_20230101_152753.jpg

I never took a picture of the tap extension but did the same thing, and then tig welded it to the tap with 2 spots. I ground them on the surface grinder, as well under cut the tap so it could thread beyond the threads.
As it was, pure luck getting it out, as the side of the threaded hole in that tube is seen. I had to make a pull rod from 1/4" round bar to be long enough as the kit was limited. And I made a simple sliding hammer from some larger scrap round drops.

**metric_taper** · Jan 3, 2023, 08:36 PM

Originally Posted by nova_robotics

I got a problem. Turns out my tool isn't quite long enough. I didn't think my CNC machine would end up agreeing with my ex-girlfriends.

So did you heat the tube up a bit to insert the mill cutter? I've never done a shrink fit.

**nova_robotics** · Jan 3, 2023, 09:22 PM

Yup. I machined it about 5 thou under. Heat it up with a torch and the shank drops right in. Then when the temperature equalizes the sleeve grabs the shank tightly. If you apply heat quickly you can remove the end mill and reuse the sleeve. I've done it with HSK40 shrink fit tool holders as well.

**DIYer** · Jan 5, 2023, 04:08 AM

Thanks nova_robotics! We've added your End Mill Extension Sleeve to our Machining category,
as well as to your builder page: nova_robotics's Homemade Tools. Your receipt:

End Mill Extension Sleeve by nova_robotics

tags: milling

**Toolmaker51** · Jan 12, 2023, 03:51 PM

Q: We've all reamed for close slip fits, such as dowels. The very closest need an air vent to allow male stay within the bore, fully seated.
Drill a tiny hole or grind narrow lengthwise flat on the cylinder.
Does that phenomena occur with shrink fit tooling?
Additionally, are same toolholders contoured inside for a positive seat and dependable length overall?

**nova_robotics** · Jan 12, 2023, 08:11 PM

Originally Posted by Toolmaker51

Q: We've all reamed for close slip fits, such as dowels. The very closest need an air vent to allow male stay within the bore, fully seated.
Drill a tiny hole or grind narrow lengthwise flat on the cylinder.
Does that phenomena occur with shrink fit tooling?
Additionally, are same toolholders contoured inside for a positive seat and dependable length overall?

I haven't had that problem. When heated this was loose enough that it basically fell in. Hotdog down a hallway. I would be worried about it being size-for-size like that. If it were tight there would be too much heat transfer and it would grab. I made a second sleeve and didn't get the dimensions quite right and that happened. It was a pain in the hole to get apart again.