Milling Melonite Treated Metal?

[redneckclimbing]

Anyone ever milled any melonite treated stainless steel? Or any other steel in the 75 -80 Rockwell range.

I have a muzzle loader with a melonite treated barrel and I need to tap two screws into the barrel so that I can mount a short section of Pic. rail to it?

Will a regular carbide end mill cut it? What about the tap?

Thanks for the advise.

 

[Pdvdh]

Melonite only hardens a very thin surface of the steel. Shouldn't be a problem for a carbide end mill. Or a tap.

I've never run an end mill in my life. I've run plenty of taps. Just saying that the melonite process hardens less than a 0.002" depth into the surface of the steel. Once you break thru the surface, you're straight back into the substrate steel as far as hardness goes.

 

[shortgrass]

The hole is not the problem,, tapping it is.. Even a carbide drill, like the ones sold specifically for scope mount applications, will work. But I'd be concerned about the tap. I'm assuming you need a 6-48 or 8-40 tapped hole or two to mount that rail. That very thin surface is still there at the edges of the hole and either of those taps are mighty fragile. A carbide tap of that size (if there is such a thing) would be very brittle. Torsional strength is not one of carbides strengths, being able stand-up to high heat is. In the past, when I used a carbide two flute drill to get through that "rock hard skin" of a Springfield and some commercial Mausers I've encountered, I've been able to anneal those 'edges', after drilling, and carefully tap the hole (new premium HS tap). I'm not sure Melonite can be annealed. I guess a Google search would be in order to find out. Not unlike case hardening, it re-enforces the rule "Make sure you have all the machine work done before treatment".

 

[Edd]

If the hard stuff is that thin, why couldn't you counterbore the hole before you tap it?

 

[J E Custom]

I have a QPQ coating on Some of my brakes, and Carbide tools hates it. So when I need to machine on/in it I have to grind the area to be machined first,

For Tapped holes, I use a small stone with a flat nose just larger than the tap and remove several Thousandths of the surface. Then it can be drilled and taped normally.If done carefully, you cant tell it was ever done.

QPQ treatment falls somewhere in the Rockwell 57 to 60 range so the Melonite should be close to the same and can be treated the same in my opinion.

J E CUSTOM

 

[shortgrass]

If the hard stuff is that thin, why couldn't you counterbore the hole before you tap it?

That's a good idea,,, as long as the counter bore is carbide, too. A carbide center drill would be the ticket.

 

[Pdvdh]

I have a QPQ coating on some of my brakes, and carbide tools hate it. So when I need to machine on/in it I have to grind the area to be machined first.

For Tapped holes, I use a small stone with a flat nose just larger than the tap and remove several Thousandths of the surface. Then it can be drilled and taped normally. If done carefully, you can't tell it was ever done.

QPQ treatment falls somewhere in the Rockwell 57 to 60 range so the Melonite should be close to the same and can be treated the same in my opinion.

J E CUSTOM

That's what I'd do if I didn't want to risk dulling an expensive carbide end mill or any other expensive cutting tool. Use a cheap stone - maybe a diamond stone. You'd only have to grind a very shallow depth over a very small area. You'd need good barrel and stone control to prevent visual damage to the surrounding surface. Even a drill press could work. If there's a will, there's a way.

 

[shortgrass]

JEs' way looks like the cheapest/easiest. I recently bought a couple of carbide center drills,, a #1 and a #3. Seems they were $20-$25 a piece verses $4-$6 for HS. Melonited S.S. can be cut with Carbide. I've done it. I didn't get a counter bore deep enough on a barrel and I noticed the bolt nose would rub very lightly after I'd torqued barrel to action. I chucked the barrel up and it cut easily with a SECO c6 insert mounted on a 1/4" Kennametal carbide shank boring bar. Hardness measured on the Rockwell tester in the shop showed 61C. It was a barrel I'd had treated at MMI Tru-Tech.

 

[Trickymissfit]

First of all anybody claiming a Rockwell figure of 75 to 80 points needs to be working for NASA! Be thinking 62/65RC.

I drilled and tapped hundreds of holes thru nitrided steel with a case of .025" to .035". Small holes are a pain, but can be done. Here's my latest method for anybody wanting to know. Best done in a Bridgeport or a good knee mill with the spindle quill clamed tight. Move the knee towards the tool. I found that a carbide 60 degree center drill worked best for me. Then went thru the pilot hole with either a Hi-Roc drill or in many cases a good Colbalt drill. When you use the center drill open the hole a few thousandths bigger than the thread O.D. I've used this method for drill & tapping #10's and 5mm without a hitch. Steels were usually 4150 or 4350 that were nitride hardened.
gary

 

[redneckclimbing]

Well heck yeah, there was advise there I didn't even fully understand! I sure do appreciate it guys.

Sounds like the easiest thing will be to grind off a few thous where the holes need to be and go from there? The pic rail will cover it all up anyway so it wouldn't even look bad when it's done.

Thanks again!

 

[Trickymissfit]

a typical center drill cuts like a two flute end mill. You can alter them to fit your needs, but you'll need access to a tool & cutter grinder. They're not as expensive as an end mill. I have in the past done the same job with a modified two flute end mill that hat the cutting faces angled to 110 degrees. This is a great idea for short shallow holes. But a real S.O.B. to regrind small diameter end mills (by the way you can buy end mills in just about any drill size). The real issue is tapping the thread. I use three and sometimes four different taps for one hole. All have the lead cut differently to get the very last thread in the hole.
gary

 

[redneckclimbing]

a typical center drill cuts like a two flute end mill. You can alter them to fit your needs, but you'll need access to a tool & cutter grinder. They're not as expensive as an end mill. I have in the past done the same job with a modified two flute end mill that hat the cutting faces angled to 110 degrees. This is a great idea for short shallow holes. But a real S.O.B. to regrind small diameter end mills (by the way you can buy end mills in just about any drill size). The real issue is tapping the thread. I use three and sometimes four different taps for one hole. All have the lead cut differently to get the very last thread in the hole.
gary

Good info on those taps! I appreciate that.

 

[Trickymissfit]

Good info on those taps! I appreciate that.

I personally like Hi-Roc drills. They're odd looking, and the first time I saw one I was not too impressed. But I soon learned the drill very nice round holes (almost look like they're reamed). Your typical two flute drill bit doesn't drill a strait hole most of the time, and is never round. There is a simple trick when just drill holes. Drill the hole about .005" or .006" undersize. Then go back thru the hole with an on size drill bit. Better yet a thousandth or so under size.

Most of us would be amazed at the quality of a typical grind job on a drill bit! Actually better said mad about the grind job! Then you get into the small sizes, and it becomes pot luck. I've seen new drill bits go .005" oversize on a quarter inch hole, and had one batch go close to .015" on a .75" diameter. I personally can't look at a .125" drill bit to see if it's right, but the shadowgraph doesn't lie! I suggest spending some extra dollars and buy a good U.S. made brand. Most drill bits are ground for soft steel, and have trouble with the typical prehardened steels that are so much in vogue these days. But you can order them in, but not at the hardware store. Then you have to change the relief for aluminum and brass. I've done everything from Micarta to Hestalloy (stay away from it!), and some serious oddballs in between. I always hated punching holes thru Ampco 18 and 22. If all goes perfect, a good and sharp cobalt drill does the job nicely. One slight hic up, and it's junk. Some metals will not allow you to push the metal off the surface (like a carbide insert does), and want you to shear the metal away. Others will work harden with carbide (Ampco bronze for one). Others just won't cut well with a carbide insert, but you change over to a diamond or ceramic, and they cut very well. And some won't cut well with anything (Hestally and Waspalloy). I've seen steels that cut well with a good tool, but literally wore a grinder wheel out after heat treat (Air Die rings a bell).

I recommend everybody get their hands on a Machinist Handbook. It a very good start in understanding why. They also do a heat treat handbook, and this one is an education in itself. There are a couple other hand books that are nice, but also very technical.

gary

 

[Wado]

I worked in a Job Shop for a few of years and we used screw machine length drill bits for most of our drilling. All the hole locations were spot drilled first and had a slightly larger dimple diameter than the bit used for the through hole or the tapped hole so there was a chamfer and the tap would start easier and there was a burr free hole. The owner was partial to Nachi spiral taps and drills and also started using thread mills on the CNC mills about the time I departed. Phased out a lot of the manual work that I was doing. There was some parts we made that had to be drilled with a sensitive drill attachment, talk about nerve wracking and time consuming. This job got put on a Tree CNC mill, hardly ever broke a bit you just had to make sure the chips stayed off of the bit and do a bit change at the right time. That CNC mill made me nervous but it sure turned out some work.