Gunsmithing Broken Reamer, need advice

[Dylanss180]

Ok guys I need some advice to see if I am doing anything wrong. I bought a rougher and finisher reamer from PTG and they are made of HSS. I made a forming die first and I pre drilled the chamber and then proceeded to single point the 1 degree taper until I only had a few thousandths left. I then started to use my chamber reamer. I used Hangstifers oil (very thick stuff used for reaming and tapping) and had the piloted reamer in the piece of 4140 at RC 32 material with a live center on the back of the reamer with a large tap handle on the reamer that I would hold.

Now this reamer has a large diameter of 1.16" at the base (This is chambering a 20mm case necked down to a 50 cal). I wanted to keep the surface feet low so I started at 50 rpm. I would take .020 deep cuts between removing the reamer and clearing the chips. The first part of the reaming was just removing material at the neck and starting at the shoulder and it was working fine. But when the flutes started cutting at the 1 degree main angle of the chamber it really was grabbing (it makes sense just because there is approx 2.7" of flute length between the base and the shoulder). I ended up slowing down the lathe to 35rpm and fed it really slow (approx .010" per minute) and it would bite so hard sometimes that the tap handle would rip out of my hands.

Ok here is the main point I am trying to convey. One of the times when it ripped out of my hands I stopped the lathe and just torqued on the handle (not actually turning the reamer to cut, but to load it up) and while I was torquing on the handle I noticed that the reamer was really flexing (approx 8 degrees). I pulled the reamer out and cleaned everything up and felt the chamber and it had no galls in it and the flutes were still sharp (This is a brand new reamer). I lubed everything up again and put the tap handle on the compound so I don't have to hold it anymore. Well, when feeding it in the reamer broke.

It was a pain in the ass getting it out but when I looked at the end of the reamer it looks to me most of the material was taken away for the flutes making the strength of the reamer itself weak. The core diameter is approx .4". I would think trying to turn a 1.1" diameter with only a .4" core is too much stress. Do you guys think that could be the case or am I just doing something wrong?



You can see that there really isn't mutch material there for the reamer to have any strength. It looks to me that it was all removed for the flutes.

 

[300sniper]

What material are you working with?

 

[Dylanss180]

What material are you working with?

4140 at rc of approx 32

 

[338RUM runner]

Call Dave at PTG and talk to him first and get some help from him, he would know how to help better than the rest of us. Just my .05

 

[flatland1]

Just my opinion, it would seem to me that flutes that long would be more likely to cause chatter. Dave Kiff is the expert here, so I'll defer to his judgement, but still....

Whatever, I use the same pre-bore method when chambering, roughing with a plain 3/8" drill, then boring the drilled hole true with a carbide boring bar. I never bore to match the case body taper; instead, I go straight in and stop boring at least .020" under the finished dia at the case body/shoulder junction when boring. Leaving less than .020" at the shoulder seems to increase the chance of chatter when starting the reamer, and I hate reamer chatter...

 

[oinco]

IMHO, that reamer design would allow for only very minimal feed and depth of cut, and I would question the accuracy/longevity attainable with that much possible flex. Of course some can make a perfect sphere with a file and a block of stock with enough time, so ymmv.

 

[ugsly]

I used to pre-bore out the chamber and run a boring bar in the make the hole perfectly round so the reamer wouldnt follow an oblong hole. I now just use my finish reamer and run coolant and pull every .100 to clean. I know there are many way of doing things and thats just the way I do it.

Casey

 

[hero's machine]

I had one do this. dave fixed it by sending me a new one as fast as possible.

 

[buffybuster]

I had one do this. dave fixed it by sending me a new one as fast as possible.

I had one do almost exactly the same thing. Clean break right at the shoulder flute, cutting the first chamber. Sent it to Dave Kiff and he replaced it right off.

 

[Dylanss180]

I have heard of people having their flutes break before, but I have never seen them completely snap in two.

 

[hero's machine]

Buffy,......that's exactly what mine did. It lasted about 2 bites.

 

[Bugholes]

What did the chips look like? I'm gonna guess powdery wiith black rings left in the chamber? If you can't pull out the reamer after a peck then it's not cutting properly

 

[Dylanss180]

What did the chips look like? I'm gonna guess powdery wiith black rings left in the chamber? If you can't pull out the reamer after a peck then it's not cutting properly

When cutting the shoulder there were actual chip flakes. but yes just before it broke I was getting powdery chips. I didn't see any black rings, but I wasn't checking that close. And yes it was hard to get it out when it was cutting the main 1 degree angle.

 

[flatland1]

Well, crap - right after I posted my reply, I started on a .30-'06 chamber, and at about the 2/3 depth point, my match reamer grabbed, breaking a chunk out of one flute, right behind the shoulder, nearly identical to the photo hero's machine posted. This is only the 2nd chamber cut (well, partially cut) with this reamer, and there was no chatter or any other abnormal behavior, when it grabbed & broke. My reamer holder handle is short enough to allow it to rotate freely without hitting the ways, so it must've broke the flute when it grabbed & snatched the holder handle out of my hand.

Hate to pull a bbl out of the spindle once it's started, so a call to PTG is the first order of business to attend to this morning. Hope Dave's got another match or Serengeti '06 reamer in stock...

 

[skeetlee]

I've had two 30br reamers brake on the shoulder first cut on each. Is really like to no why. I prebored same as always.

 

[Dylanss180]

I was on the phone with Dave at PTG and he told me that I should just use the roughing reamer all the way in until I am ready to use the finisher. Never tried that before. Any thoughts?

 

[kiff]

The odds of breaking two reamers on the same Die or Barrel are slim especially with Two reamers one with 8 flutes and the other with those heavy 6 Flutes . But it is possible especially on a 20 MM V necked down to 50 cal . That's a hell of a bite . I checked one today , The angles and edge looked good it did look like it hit something hard on the top of the shoulder . I will check the other when it gets hear . Pete said he going to take a video of him cutting a stub with your second reamer with the flute broken out of it , wont that be interesting. If it cuts the chamber its probably your material . Hell I'll even post it here for you . Thanks Dave Kiff

 

[medic727]

Coupla' things. Cutters with an even number of flutes are more likely to chatter than one with an odd number. Has to do with harmonics where the even number of flutes causing a feedback loop where the vibration builds on itself. Odd number of flutes dampent the vibration. Its' tough to tell from the OP's broken end on photo, but its' quite likely that the reamer was cracked during heat treatment or was improperly tempered making it more brittle. Reamers are tempered to point that is more brittle than most other cutting tools. Taps are another good example of this. A good way to determine this is to look at the broken surfaces under magnification. If there are shiny surfaces were the tool snapped, those are the areas where the tool was already cracked. They get shiny from the 2 surfaces rubbing against one another. The dull areas are where the material cracked catastrophically.