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Bluechip:
Hi Folks

Bernd suggested in a previous topic we start a post on reaming. Here it is.

I have trouble getting a decent finish in reamed holes. This has been going on since 1971 in my case.

I use reputable UK made reamers, not worn out, hand reamers with a taper, in a Jacobs chuck fitted in the tailstock.
The Myford has been set up with 2MT alignment bar and has no significant error. It turns parallel to .0008" in 10".
Good enough for me.

If I ream FCMS, the hole is OK. Nice smooth finish, no, or little, chatter pattern etc.
Brass and Ally, either chatter or score marks, usually both  :scratch:

Been fooling about this AM with brass, trying different degrees of cut from about .002" to .020", revs from 40 ish to 900 ish, just the same. Tried smacking it through and very slow. With & without lube. ( Rocol RTD ). I always get some marking in the bore.

Would some kind soul drop a few ideas in re: where I'm going wrong.

 

Dave BC

sbwhart:
Hi Dave

The problem may be that the reamer is too sharp try a blunt/well used one to see what you get, or taking the edge off a reamer with a stone or diamond hone.

Cheers

Stew

bogstandard:
Dave,


--- Quote ---hand reamers with a taper, in a Jacobs chuck fitted in the tailstock
--- End quote ---

If you mean a tapered lead in, and a square drive on the back end for a tap wrench.

That just might be your trouble, hand reamers are for use by hand, machine reamers are for use on a machine. Straight flutes are for thicker materials, spiral flutes are usually used on thin material to give a little bit more support.

I have just got back in from machine reaming a load of bores in brass. 3/8" bore, 23/64" pilot drill (approx 0.015" smaller), 300 RPM, no lubricant, every one perfect.

For a hand reamer, I would keep that difference to about 0.005" or even smaller.

I don't think you can run your machine slow enough to use a hand reamer. How fast can you turn a reamer if you do it by hand? Most probably about 20 RPM if you really went at it, which you don't want to do any way.


Bogs

kvom:
I'll just parrot what I've been told at school:

1) Drill 1/64" smaller for holes up to 1/4", and 1/32" smaller for larger holes.

2) Speed for reaming about 1/3 that for drilling

3) Use machine reamer, and chuck to keep as long as possible.

4) Cutting oil

5) Smooth continuous feed into the hole and out again.

Seems to work for me.

Bluechip:
Hi Stew , John, Kvom

Thanks for replies. I will try dulling a reamer to see what happens. I have one parallel reamer, 1/4" , 2 straight flutes, that does seem to be better, so I think John is right. I've always been annoyed 'cos they all work fine in FCMS.
The Myford goes down to 25 rpm ( just had to have a look  ::) ), so I'll have a go at that. As an aside, for many jobs, it doesn't matter too much. The hole is not seen usually. Irksome, 'cos I know the rough hole is there.

Maybe I should get a machine reamer or two, maybe 1/2" & 5/8", for small cylinders. If they're OK then it's not me.
Although that's usually the case  :(

Dave BC
 

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