The Breakroom > The Water Cooler

So muchfor pilot holes

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sparky961:
They are quite common in professional machine shops where I am.

https://www.google.ca/search?q=allied+spade+drill

SwarfnStuff:
Thanks Sparky,
       I learn stuff on a daily basis, never knew they existed until your post. Now I know even if I will never need one but I like the idea.
John B

AdeV:

--- Quote from: sparky961 on September 11, 2017, 09:38:14 PM ---At work, I regularly use a 1.781" diameter spade drill in 304 and 316 stainless.  No pilot hole, as spade drills really don't appreciate them.

Even though it's isn't exactly a "hobby" lathe, I can still stall it if I'm too ambitious with the feed.

--- End quote ---

Persumably you spot the hole first to make sure the spade goes in nice and straight? Or is it not a problem at that size?

Also... out of curiosity, what sort of material removal rate do you get with that drill? or to put that another way, what's a typical feed rate for it?

I looked at getting a spade drill waaay back when I was making my aluminium sump; in the end, a plain twist drill did the job, albeit slowly & with a lot of backing out for flute clearance.

sparky961:
No spotting either. Material needs to be faced, or at least fairly flat to start.

I run about 0.002 to 0.004 IPR @ 60 to 80 SFM in stainless. If the machine had more low-end torque it could be fed much harder. With through coolant this is often done without pecking. Chips don't break at this low feed rate, but the alternative is to stall the machine.

AdeV:
Presumably the SFM is measured at the edges of the spade? I'm trying to convert that into RPM in my head, without a lot of luck :D

Edit: OK, think that's between 28 and just under 38 RPM?

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