The useful "D" reamer

How timely, just yesterday I made what I think is a D reamer. Basically a D bit. A piece of 3/8" dia, W1 drill rod with a cutaway half for about 1/2". Hardened to cherry red and tempered to light yellow. Ground to in front with bottom and side clearance.

On brass did not work exactly as expected, it seized a bit, managed to finish OK with oil and backing out often.

It did not grow in dia as you experienced. I do not know what is the trick, I was thinking of "upsetting" slightly and grind/sharpen to size. Any suggestions?

Mauro

Greetings Mauro, A D bit and D reamer are the same thing. I rough turned the reamer .001 over the desired size. This turned section was about 5/8 long. The remaining length of the reamer was turned undersized so it wouldn't rub. After heat treat the reamer ended up .002 over size so I had to polish .002 from the diameter to get it to the proper size. The reamer was ground such that it was about .010 thicker than half. The front of the reamer was the only other place where it was ground. The cutting corner radius is about .030. With a D bit or reamer you will need to back out often, as you discovered. Relieving much of the reamer will help a lot to prevent seizing. If you want the reamer to straighten a hole then it should be to size long enough to keep the reamer from following the drilled hole. Don't trust the drill rod to remain straight after heat treat. For a 3/8 hole use either 7/16 or

1/2 drill rod. Face and center drill the end. Then stick the rod out of the chuck or collet as long as you want the reamer to be. Support the outboard end with a center. Turn the front section about .001 over size for about 1/2 long. Turn a relief after that about 1/4 long and about .340 diameter. Turn the remaining length about .010 oversize. After heat treat put it back into the lathe, support with a center, then finish the diameters. Only the cutting end needs to be hardened. The relief should be where the hardened part ends. ERS

That sounds an awful like what we call single flute cutters. Is there any relief angle on the side of the "reamer"? Or is it just turned round?

It's just round. That's the beauty of the tool. It will follow its own hole very well and can be made by practically anyone. A major drawback is that since it fits snugly in the hole it may bind if not kept properly lubed or if the work heats up and then cools around the tool. So the tool must be withdrawn often to avoid seizing in the hole. This makes it a good tool for limited time, limited budgets and limited use. ERS

Thanks, I'm going to give that a try.

snipped the good info..

A couple of ?'s if I may.

Is it best to harden when in the round and grind the flat side with the bench grinder or mill the flat then harden? Is it used fully hardened or tempered? Is there a best lead angle or is it left faced ie. flat?

I made one once to make a bullet sizing die and was surprised that it worked so well, but spent a good bit of time grinding to get it to cut well, IIRC.

Thanks

ED

Greetings ED, I like to grind completely after hardening. This is because I finish sizing the tool after hardening and I'm using sand paper to finish. However, sometimes I will grind the diameter of the tool. If I'm going to do that then I may rough grind the flat on the tool before heat treat. Kinda depends on my mood. If it's a large diameter tool then rough grinding before hardening and finish grinding the diameter and flat after hardening is the best. And yes, the tools do get tempered. Barely though, they need to be hard. ERS

Thanks, do you put any sort of a chamfer on the leading edge? I've heard of guys making one off chamber reamers like this. Amazing what one can do with a bit of ambition.

ED

I put a radius on the leading edge. The tool spins clockwise like a regular reamer. Looking down onto the tool the front is ground at about 5 degrees with the left side proud. This left corner gets the radius. A chamfer would work too I suppose, but I've always used a radius. These tools have always left a good finish. ERS