What is in a #1 - #60 chucking reamer set?

[WobblyHand]

Drill undersize. Try 1/16" under first ( 3/16" ) then 1/32 under (11/32"). Finally ream to 3/8". Works well.

The idea is to drill the largest hole you can that is 1/16" undersize. Then 1/32" undersize. Reason for this is to prevent as much as possible drill wander from tiny drills. If you drill 3/8 in the beginning, it already maybe oversized, and there will be nothing to ream!

 

[MrWhoopee]

If you intend to make a hole that you will eventually ream with a 3/8" reamer then would you first drill the hole out with a 3/8" drill or a drill slightly less in diameter?

Drill 1/64" undersize. Just be sure that the drilled hole is on location. Best practice is drill, bore then ream. Not always feasible or necessary.

 

[macardoso]

I've always used the 97% of diameter rule for a reamer pre-drill.

Reamer Diameter * 0.97, then round to nearest drill you have (fractional, letter, number, or metric).

You can actually vary the final ream diameter by over or undersizing the pre-drill. I believe a smaller start hole yields a bigger reamed hole and vice versa. The diameter only varies within a couple of tenths, but it can help if you are shooting for a particular fit.

 

[MrWhoopee]

Speaking of reamer sets.
Has anyone used any of these? $15.65 with free shipping from China

4pcs Chucking Reamer H7 Accuracy HSS 6 Straight Flutes 1/8" 3/16" 1/4" 5/16" | eBay

Find many great new & used options and get the best deals for 4pcs Chucking Reamer H7 Accuracy HSS 6 Straight Flutes 1/8" 3/16" 1/4" 5/16" at the best online prices at eBay! Free shipping for many products!

www.ebay.com

I had time to check these reamers out today. Appearance-wise they are nicely finished 6-flute reamers. The size is etched on the shank in fractional inches except the 1/4" which says 6.35mm. I measured the diameter across all 3 pairs of flutes looking for variation (there was none), then drilled and reamed a hole with each in some free machining steel. The pilot holes were drilled 1/64" undersize then reamed at about 100 rpm with black oil.
I had no way to check the holes except by trying various pins around the shop. Here's what I found. The first number is the measurement of the reamer. The second number is the size of the largest pin that would fit. If that number has a plus, it indicates that the pin was still a little loose.

1/8" .1253 .1245+
3/16" .1880 .1894
1/4" .2507 .2502+
5/16 .3131 .3129

I had dowel pins to check all but the 1/8, so I had nothing within .0002 to check that one.
All of them cut freely and produced a good finish. With a little use, they will probably settle in a few tenths smaller.


I can't complain.