Turning Bolts with HSS?

[ErichKeane]

Hi all-
I have been working on a project (tang ends for my MT4 center/drill chuck), and had an interesting thing happen that I was curious about. I needed a threaded section on part, so my design was to take some bolts and turn down all but the end so that I could loctite that into a larger section, which would have the actual tang part.

My first one worked perfectly, the 5/8-16 bolt I bought was long enough to fit in the 3 jaw and stay centered, and turning it down went very easily. I'd cut the bolt head off with the bandsaw, and had no problems. The bolt was the cheapest 5/8-16 bolt they had, so I suspect it was grade 2.

However, my second one was m16x1.5, which was harder to find. My local Ace hardware only had Class 8.8, which is apparently a "medium carbon steel". The bolt I had wasn't particularly long, so holding it in my 3 jaw was quite difficult. Additionally, I needed the length under the head, so I was going to turn it down.

I got about 1/2 way through the head, and the HSS bit stopped cutting. It was cutting fine for a while, but then it seemed that the bolt was "burning" the HSS instead! The 'burned' out spot was dark blue. I reground my bit, and tried a different one with the same result.

Did I just work-harden my bolt, or was it too hard in the first place?

I've since ordered some zinc coated Class 4.8 all-thread (I had to buy a meter of it!) that will hopefully turn easier, but I would love to know what I did wrong!

 

[ttabbal]

My guess is that you were running fast for the HSS on that material. That eventually dulled the tool causing it to rub rather than cut. That could well have work hardened it. I have some steel here that does that with HSS. To get decent speed and finish I need to use good carbide inserts. The cheap ones from China aren't up to it either.

 

[ErichKeane]

My guess is that you were running fast for the HSS on that material. That eventually dulled the tool causing it to rub rather than cut. That could well have work hardened it. I have some steel here that does that with HSS. To get decent speed and finish I need to use good carbide inserts. The cheap ones from China aren't up to it either.

Ah, interesting. I was runniing ~200 RPM (I think). I don't really have any carbide since my lathe tops out at 536 RPM, so I figure I wouldn't use it much.

When I suspected work hardening, I took the bolt head to the grinder and ground off ~1/16" all around, and tried again, but ended up immediately dulling/rubbing my newly ground tools. My HSS are some cheap chinese set of pre-ground ones that I got to get myself started, so perhaps it is just cheap HSS on top of it.

Oh well, something to know for the future

 

[benmychree]

MoMax Cobalt likely would have worked better ----

 

[RJSakowski]

Ah, interesting. I was runniing ~200 RPM (I think). I don't really have any carbide since my lathe tops out at 536 RPM, so I figure I wouldn't use it much.

When I suspected work hardening, I took the bolt head to the grinder and ground off ~1/16" all around, and tried again, but ended up immediately dulling/rubbing my newly ground tools. My HSS are some cheap chinese set of pre-ground ones that I got to get myself started, so perhaps it is just cheap HSS on top of it.

Oh well, something to know for the future

I have seen Chinese HSS that is actually carbon steel. I would spark test it. M2 HSS has an reddish orange spark with no branching. Carbon steel has a yellow spark with branching.

 

[Bob Korves]

Metric grade 8.8 bolts are roughly equivalent to US grade 5 bolts. They are not that hard, and should machine well with HSS. However, import bolts are all over the chart. Many of them are labeled as whatever they wish and without actually using that grade of steel. The Chinese do not really enforce any of this, so caveat emptor, let the buyer beware. Chinese bolts in inch sizes with SAE American markings are in the same category. Buy ones known to be good quality and with good quality control, or you may have unexpected failures. For many applications it doesn't really make much difference, but for high strength applications that must not fail, it is critical that quality fasteners from a known good source are used (there are also imposters out there...)

 

[ErichKeane]

I have seen Chinese HSS that is actually carbon steel. I would spark test it. M2 HSS has an reddish orange spark with no branching. Carbon steel has a yellow spark with branching.

Good to know! I'll have to take a look. This is the set I got: https://www.ebay.com/itm/HSS-Lathe-...k-Metalworking-Turning-Threading/332747011341

Apparently out of India. I was looking for a couple of HSS tools to start with (I'd been using 3/8" carbide holders previously with my 10" logan, but the 16" machine doesn't go that fast, and 3/8" holders would be lost). They've done alright until now, so I was surprised to see this problem.

Metric grade 8.8 bolts are roughly equivalent to US grade 5 bolts. They are not that hard, and should machine well with HSS. However, import bolts are all over the chart. Many of them are labeled as whatever they wish and without actually using that grade of steel. The Chinese do not really enforce any of this, so caveat emptor, let the buyer beware. Chinese bolts in inch sizes with SAE American markings are in the same category. Buy ones known to be good quality and with good quality control, or you may have unexpected failures. For many applications it doesn't really make much difference, but for high strength applications that must not fail, it is critical that quality fasteners from a known good source are used (there are also imposters out there...)

Thats good to know as well. I know a lot of chinese metal stuff ends up having strange hard spots in it, so perhaps this was that as well. I was having a heck of a time holding it in the 3 jaw anyway, so this just made me give up and buy threaded rod. My normal source for bolts is just Ace Hardware's bins, which I suspect are just chinese stuff, so thats probably what I got.

 

[pontiac428]

I had the same experience with a china black oxide socket head cap screw that I wanted to rebate the head on. Switching to carbide cut it, but not pretty. I ended up finding another bolt.

Work hardening is a little different, because if you plunge through it and get an aggressive depth of cut going it usually goes okay.

Edit: I bought a few stashes of USA HSS blanks as new, old stock on eBay. Cobalt is a bonus. No comparison to china or india quality.

 

[mikey]

Hmm, you could also just screw cut what you need from known round stock, no?

 

[ErichKeane]

Hmm, you could also just screw cut what you need from known round stock, no?

My lathe is from 1941, so it only cuts imperial It seemed cheaper/easier to buy a bolt and cut it out of there instead of buying a die to cut the thread.

I could have single-pointed the 5/8-16 part presumably, but I was already going to do this for the metric one so I did both.