Pre-Ream Drill Size Chart PDF
OK -- say I want a final hole size of 0.75 inches; which drill bit and reamer do I select ?
OK -- say I want a final hole size of 0.75 inches; which drill bit and reamer do I select ?
How to Read Pre-Ream Drill Size Chart ?
- Thread starter Merkava_4
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So according to the chart, if I'm gonna use a 3/4'' reamer, I need to use an 18.5mm drill bit first; correct ?
Are you guys afraid to click on the link or something ?
Why the mixing of Imperial and metric ?
Beats the heck outta me; I didn't make the chart.
They are using metric where the closest size to the hole needed cant be met with inch.
If you want 2% material left for reaming you need a .7350 hole and an 18.5 mm drill will do that. If you want 3% a .7275 hole is needed with an 18.3 bit.
For steel and hard metals you use 2%, for non ferrous and cast iron 3%. An 18.5 bit is going to be cheaper than an 18.3 for sure. What part do want to size that big? On car engines its mostly valve guides and wrist pin bushings.
If you want 2% material left for reaming you need a .7350 hole and an 18.5 mm drill will do that. If you want 3% a .7275 hole is needed with an 18.3 bit.
For steel and hard metals you use 2%, for non ferrous and cast iron 3%. An 18.5 bit is going to be cheaper than an 18.3 for sure. What part do want to size that big? On car engines its mostly valve guides and wrist pin bushings.
I know the answer, and I'd like to post it here.
But then I'd feel like I'm being honest for nothing.
But then I'd feel like I'm being honest for nothing.
JHZR2
Staff member
Originally Posted By: KzMitch
I know the answer, and I'd like to post it here.
But then I'd feel like I'm being honest for nothing.
HAHAHAHA!!!!
I know the answer, and I'd like to post it here.
But then I'd feel like I'm being honest for nothing.
HAHAHAHA!!!!
I have this same exact chart in sticky magnet form on my machinists toolbox at home. I always use digital dial calipers on the drill bit on a finish drill prior to reaming to verify size even it the bit is clearly marked. The caliper I have will convert to decimal, fractional, numerical or letter sizes. If you are a thousandth off to the small side prior to reaming, its no big deal 99% of the time.
Originally Posted By: Trav
They are using metric where the closest size to the hole needed cant be met with inch.
If you want 2% material left for reaming you need a .7350 hole and an 18.5 mm drill will do that. If you want 3% a .7275 hole is needed with an 18.3 bit.
For steel and hard metals you use 2%, for non ferrous and cast iron 3%. An 18.5 bit is going to be cheaper than an 18.3 for sure. What part do want to size that big? On car engines its mostly valve guides and wrist pin bushings.
Fantastic! Thank you sir! Thank you sir! Thank you sir!
They are using metric where the closest size to the hole needed cant be met with inch.
If you want 2% material left for reaming you need a .7350 hole and an 18.5 mm drill will do that. If you want 3% a .7275 hole is needed with an 18.3 bit.
For steel and hard metals you use 2%, for non ferrous and cast iron 3%. An 18.5 bit is going to be cheaper than an 18.3 for sure. What part do want to size that big? On car engines its mostly valve guides and wrist pin bushings.
Fantastic! Thank you sir! Thank you sir! Thank you sir!
depends on how true to size your drills actually drill their hole. Not hard for a bit to drill a hole 2% oversize, most do cut oversize. Drilling small and boring to size before reaming is a more precise option.
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