Hot roll work hardening like SS

[RB211]

I started working on steel with lower RPM after watching a bunch of the early Keith Fenner videos. And yep, drills and end mills both last longer turning at lower than the tables suggest. Of course the tables are listing the maximum speeds so commercial shops can blend process time against tool life to get the best bang for the buck. But as a hobbyist the best bang for the buck for me is more of a focus on the tool life or time between sharpenings. So the slower within reason the better for tool life.

RB211, so you were running slower than the typical maximum for this situation? I'd guess a hard inclusion as mentioned. I'm not sure what they are doing to re-form the scrap into new stock but I'm guessing that whatever the process they don't take much time or effort to mix things around or let things diffuse and even it up.

By the last two holes I had slowed things down a lot and kept a constant feed

[old mart]

There are usually plenty of the straight shank carbide tipped masonary drills left over from when SDS took over to sharpen into very good drills for that ****ty steel. Their advantage is cheapness and not being brittle like solid carbide drills are.

[Dan Dubeau]

Sometimes you have to slow down to go faster. In a perfect world, the heat should be carried away with the chip. If you're putting heat into the work piece you're rubbing/causing friction. Either by running the spindle too fast, or by not feeding enough. Coolant/oil helps tremendously too, to carry heat away, and lubricate the cutting edge. For most people it's running to high of an RPM for HSS. It's a very common mistake I see over and over. SFM and chipload #'s exist for every material/tooling combination known to man. I know most manual machinists fly by the seat of the pants most of the time (I do too), but it's helpful every once in a while to re calibrate yourself to ideal parameters when results aren't what you expect. All that said, sometimes the material is just ****, and you have to adjust.

[BobH]

There are usually plenty of the straight shank carbide tipped masonary drills left over from when SDS took over to sharpen into very good drills for that ****ty steel. Their advantage is cheapness and not being brittle like solid carbide drills are.

Ok, you got me. How do you sharpen a masonry drill to cut hard steel?

[Bented]

Using Bridgeport, manual. I guess I dicked up.

There is always a very short dwell at the bottom of a blind hole as the drives decelerate at the bottom then accelerate in the opposite direction, have never found this to be problematic.

[RB211]

There is always a very short dwell at the bottom of a blind hole as the drives decelerate at the bottom then accelerate in the opposite direction, have never found this to be problematic.

I wasn't even using the power feed, and it was a through hole. Hmm, not even using the convenience features of my tool, silly me.

[davidwdyer]

Ok, you got me. How do you sharpen a masonry drill to cut hard steel?

You use a wheel with embedded diamond and some lubricant, either oil or water. Maybe about 300 grit for a smooth finish. They should sharpen up pretty quickly.

[rkepler]

It's always hit and miss when you're machining a steel made for architectural purposes - A36 is made to a strength specification and not at all to a machinability specification. Same for rebar. Both are usually machinable because (I suspect) they hit the low end of the spec but when they hit the high end of the spec or have some odd inclusion all bets are off.

I once had a chunk of 1 1/2 3/16 angle that needed half a dozen 4-40 holes. All but one went in fine, the last cost 3-4 drills and a couple of taps. I finally drilled it out to 1/2", TIG'd in a 1018 plug and cleaned it up both sides with a Foredom *then* drilled and tapped the 1018 with no fuss.

[J Tiers]

I've never understood the "inclusions" thing.

Most of the rebar etc is said to be made from remelt, but that's the point..... It was melted, and then poured out at least once (if they use a strand casting method) which should melt everything in the charge, and mix it up reasonably well.

The stories about finding a ball bearing unmelted in a piece of steel make little sense. A small piece like that should have easily been melted when the rest of the charge melted, it is unlikely to remain solid and distinct. Maybe if it is not steel, but something with a significantly higher melting point that got into the charge, then it might survive through the process.

I suppose it is "possible" to have areas of different composition. One way is if it is first poured as an ingot, then re-heated and rolled without "cropping" the "segregated" areas of the ingot, then there could be some wildly different areas with certain elements in totally different composition from the rest of the ingot, and they may get rolled out in part of the material that is processed.

Some elements tend to not "freeze" with the main part of the ingot, and show up in higher concentration (segregated) in the last parts to freeze Mostly those are cut off and thrown in with scrap in a later batch. I suppose if the remelt operation does not do that, there may be areas that have different properties. I just have a problem with the "I found a ball bearing", or "I found an unmelted nut" etc.