Reamer question for the expert.

[Metal Butcher]

It drives me just nuts that reamers are much longer than the drill bits I use to drill holes undersized for reaming!

I find myself stopped short by lacking chuck clearance during the process, and resorting to shank amputation of the reamer in my mini chop saw.

Is there an acceptable reason for this insanity? ???

-MB

 

[Seanol]

Just from what I have read, The reamer is longer to allow it to "float" so it will cut properly.

Hope that helps,
Sean

 

[Twmaster]

Explain "float" please.

 

[mklotz]

I've heard that too along with the admonition to hold the reamer by the tip of the shank to give it (angular) freedom to "wiggle".

I'm certainly no expert but it all sounds like recycled hay to me. I've reamed a host of holes with the reamer held as one would hold a drill and they've all come out on size. Plus, if reamer wiggle were really so important, why wouldn't every cutting tool catalogue include a collection of floating reamer holders? As it is, you pretty much have to make your own if you want one.

 

[Metal Butcher]

Sounds reasonable to me, and got me to think. On a few reamed holes like say, a 1/2" hole 1-1/4" deep, I noticed the first 1/4" is slightly (.0005") over size. This is probably due to chuck run out. Its time for a new, and hopefully more accurate chuck.

Thanks for all your help. It makes sense now. But, I'll still need to continue with the amputations. ;D

-MB

 

[Stan]

If you ream immediately after drilling, without removing the stock from the chuck then an oversize hole is more likely to be be the tailstock off center or a drill chuck that is bent or off center.

 

[Metal Butcher]

If you ream immediately after drilling, without removing the stock from the chuck then an oversize hole is more likely to be be the tailstock off center or a drill chuck that is bent or off center.

Actually, the slight bell mouthing I noticed a few times was at the starting end of reaming I did in the mill using an undisturbed set up.

-MB

 

[Stan]

A bent reamer?

 

[cba]

Could it be, that the drilled hole is already bellmouthed to a larger diameter then the reamer? Twist drills sometimes do that. In industry, a twist drill is often followedby a borer before reaming holes that need be very accurate. A borer is similar to a twist drill but with more than two flutes. Some borers may look more like roughing reamers. Lets say a 10mm hole would be drilled to 9.7mm, then bored out to 9.9mm, and finally reamed to 10mm.

Also, there are hand reamers and machine reamers. The former are longer and have a long tapered lead-inand a square at the end of the shaft, like a tap. Machine reamers are usually overall shorter with no lead-in, just a short chamfer. For home use I prefer hand reamers, because I can use them by hand OR in lathe/mill/drill press. Whilst machine reamers are only good in a machine. Means I only need to own half as many reamers.

Chris

PS: It also depends what material you are reaming. For example, reaming into bronze usually produces an undersize hole.