View Full Version : More Hardened Stainless

10-12-2010, 12:01 AM
Yes, this has finally reared its ugly head at my place. I'm trying to repurpose some HF calipers to be a DRO on a wood planer. Tried drilling attachment holes in the jaws, and eventually gnawed my way through one jaw. The second jaw is giving me even more headaches. I've rounded off several center drills, and resharpened several twist drills, but don't seem to be making any more progress. I've already tried starting from the other side, too. I thought I was running slow enough and feeding fast enough to avoid this problem on the second jaw, but obviously not.

So, given that predicament, what are my options? Grind with a very small stone to grind the hardened steel away? Go buy a carbide or some other drill bit? Use the calipers for something else and buy another pair for $10 (that actually doesn't sound like a terrible idea)?

10-12-2010, 12:12 AM
The SFM for hardened steels is really slow, like 20 SFM.

You can also try a cobalt bit, and although I think it is technically slightly softer, it takes heat much better. Failing that, go with carbide.

10-12-2010, 01:21 AM
Don't bother drilling. Just make up a clamp arrangement to secure the jaws.

doctor demo
10-12-2010, 01:50 AM
Ya might be able to get through it with carbide.


10-12-2010, 02:36 AM
Use the two existing screw holes that hold the depth probe in place for mounting one end of the rule and peel off the metric/whitworth thread chart on the back of the sliding part to access the screw holes underneath. No new holes needed. Or use a clamp.

If you really want to drill, you can try spot anealling:
Note that the heat may damage the printed circuit scale or the electronics board even though stainless is a poor heat conductor (it is pretty thick).

Your surface speeds may be too high, as suggested, and a heavy enough feed so you cut rather than rub.

Use a carbide drill bit, if available. Masonry drills are used sometimes if you don't have proper carbide drills but you have to keep them cool or the braze joint will separate. It helps to modify the edge a bit.

You can also try a proceedure similar to the spot anealling, but with abrasive slurry. slow.

Use a center cutting carbide end mill.

10-12-2010, 12:10 PM
All you have to do is get a carbide spade drill the size you want. It will walk right through. Run dry with no coolant or oil. You will be amazed at how easy it is. Run around 250 to 400 RPM.

10-12-2010, 02:13 PM
Looks like a carbide bit is in my future. I'll see about going that route.

I did try grinding, but that didn't seem to help. I thought about jaw clamps, but their shape doesn't really make that an easy task. Using existing holes would make the brackets pretty large and awkward.

I find it interesting that I was able to get through the fixed jaw with only some anguish, but the movable jaw is a nightmare.

Dr Stan
10-12-2010, 02:57 PM
Do you have a buddy with access to a ram type EDM machine(aka die sinker)? Even one of the old tap burners would still make a usable hole.

10-12-2010, 08:11 PM
I did a similar thing attaching a digital caliper back when I had my Rockwell Lathe. Drilled the hole with a carbide drill, and then a carbide countersink, both borrowed for the job. Of course I put a tiny chip in the countersink, so now I own it. :o But generally it went quite easy with the right bits.

10-12-2010, 08:18 PM
Just get the carbide spade drill. Any fancy stuff like spot annealing might screw up the caliper. I've drilled calipers myself,no problem with spade drill.

10-12-2010, 08:21 PM
Get a mason bit with carbide tips. This is how I drilled my HF calipers for the same purpose. Carbide drills cut these like butter.

10-12-2010, 08:25 PM
What I used was something I hear referred to as a "Hi-Roc" (no idea on spelling) drill. Looks like a small sharpened carbide bar of the correct size, but has a single "flute" like a 45* pie notch straight up the side. No spiral, no "rake", and just a "fuzz" of clearance. These seem to be very inexpensive (for carbide tooling) and readily available in the smaller sizes. But you must have a (near) 100% rigid setup and you need very high spindle speeds with very nearly no run out (no drill chucks!).