www.MG42.us

So I made the first mistake of trying to weld up my receiver myself. Needless to say my amature welding skills have presented me with countless problems. I know I know, I shoulda spent the money to get it done professionally, but thats just not me. I always have to learn the hard way.

Tonight I made mistake number 2......tried to drill the bolt myself....

I chucked up my brand new cobalt drill bit, filled the bolt with cutting fluid and lowered the drill press. What ensued was 30 minutes of smoke and swearing. Even with the cutting fluid, the bolt got so hot that it actually changed color. (the metal looks like I put a torch to it and case hardened it) At this point I figured the part was trashed so I figured I was gonna contine just to prove a point. I MELTED 3 more drill bits. As in RED HOT and melted. Good thing I ordered a spare. (That one is going to a machine shop tomorrow!) The entire garage and my some of my house still stinks of burnt cutting fluid. THat bolt is indestructable!

The way i drilled my bolts is: I heated the back of the bolt up with a torch and let it cool slowly. this takes the hardness out of that area . be careful about heating and try and isolate the back area only. the drill shouldnt have any problems after that. when your done welding everything up , i re-hardened my bolt with Kasenit .john

I had to go buy a carbide drill bit to drill thru mine. That bit cost around $25 and even using a carbide bit it only lasted long enough to drill the FP wedge and the feed stud in the rear of the bolt.
Colbalt bits would barely scratch the surface.

Bolts and bolt parts are pretty hard, best to use a centercutting carbide end mill. You must hold the piece you're drilling so that it does not move at all and run the drill press as fast as it will go. I run small to mid sized carbide at 4000+ rpm in my mill. Wear eye protection!!! If your drill press doesn't have too much runout, you'll have a nice, clean hole. Too much runout and you'll shatter the end mill, then take the parts to a shop. Try to get an MSC or an Enco monthly flier for the discounted prices, I use Atrix end mills and find that they are just great. Lon

Scott

I found out a long time ago what my limitations are. Welding and machine work are two of them. . Best thing to do is box it up and send it out. And kick back and have a beer.

TC

I bought the carbide drill in preparation to rework the bolt, thought about it for several months and ended up shipping it off to have it drilled, extension welded, and firing pin. In other words a completed bolt assembly ready to drop in. My list of things to do is getting shorter. I have a feeling that when I finally get out to the range with it I will have another list of things to tweak.

Ah yes the glass-hard bolt! I had one of those too. I assume you mean the "bolt locking wedge". I went through an entire range of drill bits in that size range! All I can say is, get a drill sharpener and keep at it. And have plenty of spares!!!! Seriously, buy at least a half-dozen of that size so you aren't dead in the water if the bit and its spare both break!

And yes, you are correct that you are trashing the bit when you let it get that hot. You're just running up your electric bill to make heat. Cut until it dulls, resharpen, cut some more. You'll take of a little bit at a time, and yes it will be slow-going, but you can drill through them. At least I did. Don't bother resharpening those bits that were red-hot, they are beyond saving, unless you cut them real short.

The slow-heat is annealing the bolt, which removes the temper. You should consider re-tempering it when you're done. Otherwise it could peen itself out of shape as it bangs against the roller locks.

The smaller the drill the FASTER it needs to spin. Most hand held drill motors will not go high enough. Plenty of oil and don't just bear down on it. Carbide works best.

Try the carbide center cutting end mill, you'll not be sorry. Lon

I took the wedge thingy (official German name!) to a machine shop today. As soon as I told him it was hardened steel, he cringed. He looked at it painfully for a few minutes and said, "well, I dunno, Ill try...' I explained to him that it was totally 'do-able' and plenty of guys have done it in the past. He again winced and walked off with my part. I hope this guy doesnt ruin my wedgy thingamobob. ( unofficial German nickname for said part)

You can drill through the wedge. But you need a carbide bit. Cobalt just won't cut it. A little play on words there. I didn't have a problem drilling through my wedge with a carbide bit and plenty of cutting oil. The cutting oil helps keep the bit cool.
BTW, I bought my carbide bits from the Carbide Depot. They have metric carbide bits. IIRC, I got the 4.5mm and 5.5mm bits. Their prices are very reasonable. If I want carbide bits that's where I buy them.
I must admit I couldn't figure out at first why he was drilling into the bolt. What hole do you need that you have to drill a hole in the bolt carrier.

You have to drill thru the bolt roller stud as well, right? As per the tutorial on this site?

Well, yes, but that isn't the bolt. Which had me wondering. The bolt stud is usually replaced with another assembly like panacea's. Which is what I have on my bolt. Still, in all, by usinga carbide bit you could drill through the original bolt stud.
I gave up long ago on using HSS drill bits. Now I use cobalt or carbide depending on the material to be drilled. Like I said before, any time you're drilling into steel, you should use Tap Magic or a similar product. It makes a world of difference in the efficiency of the operation. The same goes for tapping.
Years ago I was working in a cabinet shop. The boss was trying to drill through some angle iron. He was having a hell of a time. He was burning up drill bits. So I reached into my goody bag and handed him a container of cutting oil. The look on his face when the drill breezed through the metal was wonderful to behold. It didn't take long to have cutting oil stocked in the shop after that.
And please don't think to use 3in1 oil. That's a lubricating oil, not a cutting oil. The same goes for using WD40. Some of the best cutting oil I ever used had lard in it. It smelled like bacon frying when I used it.
I used to make custom knives. I used mostly 440C stainless or 154CM. Wasn't no way I could drill through that stuff unless I used a slow speed and cutting oil. I burnt up a few bits until I got educated.

I bought my can of Tap Magic at ACE hardware, use it all the time when drilling and tapping. I have several sets of drill bits, 2 sets (118 pcs) of HF titanium coated HSS, one set I canibilize for use for pins and all around drilling the second set is for when the size I need is no longer in the first set. Also a 118 pcs colbalt set. BTW, I have found that the HF drill bit sets have a lot of real sharp bits and some dull bits mixed up in one set, in all I have found these bits quite useable. Sharpen the the dull ones with a Drill Doctor. I do not have many carbide bits, just the few needed for this MG 42 build (1/4 and 3/16).

Bil wrote:MMM Bacon frying-burnt bits arrrrrr drool... ---bil

Those bits may smell good but I wouldn't want them served up with my eggs. A little hard on the teeth. As it is I just got back from the dentist. I had a wisdom tooth pulled. Damn thing decided to go Krakatoa on me this week. Ah relief. So here I sit with a piece of gauze in my mouth and my wallet a lot lighter, replying to rainbow bil.
BTW, I used the metric carbide bits to drill the locking wedge for my modified type firing pin design. As I said before, they drilled through the wedge like it was butter.

Hey, just to make sure I did this right.....I welded the feed stud to the bolt body. Bottom and top. Now I drill the feed stud to accept the firing pin, right?