D Bits revisited

[Chuck in E. TN]

 I need to make a 'D bit' to ream a bearing for a connecting rod. I purchased 1/4" O1 drill rod for this purpose. This is my first "D bit", as well as my first reamed hole.
I cut a 3" piece, chucked it in the lathe and faced the ends. Next, I placed the blank in my mill vise on a paralell and attempted to mill to 1/2 the diameter. I touched the mill cutter to the top, zeroed the Z axis DRO, and lowered the Z axis to .125, locked it, and milled the blank for approximately 1/2". The bearing is 1/4" thick brass. When I removed the blank from the mill vise it measures .118 on the "D" part. Is this going to work? How critical is this thickness to the accuracy of the reamed hole? Do I need to try again?
 Chuck

[Country Bubba]

Chuck,
IF your rod was actually .2500" dia to begin with, and if you now have .118" left, this means the diameter is now .2496" .

IF your starting rod diameter is less than .2500", then it will be even smaller. Everything depends on your tolerances. This just might work and if it is to small, you can always make one a bit bigger, but sure can't go the other way.

HTH

[Chuck in E. TN]

Chuck,
IF your rod was actually .2500" dia to begin with, and if you now have .118" left, this means the diameter is now .2496" .

I'm not sure what you mean. Looking at the end of the bit that was milled, it looks like a D, and measures .118 from the flat to the fattest part of the D shape. The drill rod measures .2495 as it came from the store.
 

[Country Bubba]

Chuck,
Hopefully this "sketch" of the end view of the rod will help:
If you start with a rod that is .2495" dia and remove a .125section so the remaining thickness of the D is .118", the diameter of the flat on the D will be .2491" as opposed to what I previously posted as I "assumed" a diameter of .2500" as the starting diameter.

[andyf]

Chuck, are you trying to say that you wanted to mill down to a diameter of the drill rod  (in other words, down to the half-way line) but your result seems to show you went a bit too far so that, looking at the end, you've got a bit less than a semicircle left in your D?

I seem to recall that the D should be a bit more or a bit less than a semicircle, but can't for the life of me remember which.

Maybe it would be easiest to harden and temper what you've got, and try it in a bit of scrap brass. Then reverse it and try the shank end (or the remainder of the drill rod you cut the required length from) to see if a 0.2495" diameter rod fits without undue looseness.

Andy

[Chuck in E. TN]

Andy I did just that. Mistake #1, I tried to harden the reamer in water, and didn't test it with a file. I tried reaming an 15/64" hole and distorted the reamer. I did ream a 'D' sized hole(.246") and it was a slip fit for another piece of drill rod, so I'm close. I also made a reamer with a beveled end and it worked better. I'll try again tomorrow with both styles, but hardening in oil and testing the hardness first.
Thanks for all the input.
Chuck

[Fergus OMore]

I notice that you are 'shotgunning' again for advice from various fora.  You'll get confused- and some of us peeved!

The first thing is to see what total diameter that your set up gives. in other words, your bit of silver steel may be 0.250" but it may be cutting larger because of the inaccuracy of your chuck. So we don't know what THAT figure is- but that is the diameter that you will cut- and not 0.250" So you have to reduce your embryo D bit to the size that YOU want,. It is only then that remove the metal to half the cutting edge-- and then the nose edge of say 5 degrees.

And remember that you don't fiddle about by taking the bit out of the chuck- to fiddle about with tempering or whatever. You stand a 100% chance that you will hit the wrong setting that you have eastablished with so much difficulty.

I'd settle for grinding but other others may differ. This, however, is what a good tool maker will advise.

-----------------------------------------------------------------------------------------------

Battle bowlers on, toothbrushes at the slope, kit bags will not be worn. Stand by your boots with your beds in your hand!

Norman

[Chuck in E. TN]

Well, Norman, I can ask for advise, but I don't have to take it. I often get quite a chuckle from some of the responses I get. I firmly believe that the wider exposure my question gets, the more likely I'll get a response that I can understand and implement.I usually remember to thank folks for their input, wether I utilize it or not. Forgive me all if I do forget to thank you. I ask questions to get an answer, as the often quoted "The only dumb question is one not asked..." says. I have to sepatate the usefull (to me) from the crap. Folks of all experience levels and background are on several forums, and I would feel I was missing something if I didn't avail myself of that variety.
I learn best by hands on experience. I don't have anyone near me that can show me how to do something, so I must rely on a variety forum explanations to get the 'light' turned on. To each his own... Don't take it to hard, I won't be upset if you don't respond to my questions. Enough said.
Chuck
Chuck

[75Plus]

Chuck, here are a couple of posts that may be useful. I knew that Bogs had posted something about "D" bits but it took a while to find it. Unfortunately he has removed all the pictures.

http://madmodder.net/index.php/topic,2265.msg23824.html#msg23824

http://madmodder.net/index.php/topic,2312.msg24257.html#msg24257

Joe

[Chuck in E. TN]

Thanks for the link, Joe. I read that post when it was current and even coppied it to a word document to save. Unfortunately, I stored the only copy on a usb hard drive and it has died! Lost several years of data with that crash. John(Bogs) has moved to another forum and possibly could be persuaded to repost the thread there.
I save stuff like that even if I don't use it for a while. Thats the case with my quest for info on D bits again. I had the info, didn't use it, lost it, and now need to make a D bit.
Chuck
edit: John(Bogs) has actually contributed to a thread on D bits on MEM

[DavidA]

Chuck,

Have you actually measured the drill rod with a mic ?
I don't see a reference to this . Surely you're not just asuming that because it is 1/4" rod that it is 0.250" in diameter.

Dave.

[Fergus OMore]

Oh, Chuck

'Pelmanism' is what you want- write the name down before you forget it

It's what I use.