So muchfor pilot holes

[Will_D]

I always thought you spooted a hole and o[pened it up with a seies of drills to finasl size!

Not here:

Warning this is about weapon making!!

https://www.youtube.com/watch?v=J_hQcIBbPME

Its an awesome series of videos about cnc machining ally

About 27 mins in he drills 3/4 holes straight in

[Pete.]

I always thought you spooted a hole and o[pened it up with a seies of drills to finasl size!

Nope, pilot hole at 1/4-1/3 size then drill the hole. Stepping-up in small sizes is a good way to snag & snap the drill especially if the work is not fixed down.

[awemawson]

Agreed Pete. But when people are using low powered machines at or above their capacity it's sometimes necessary to step up to reduce the power needed to drill the hole.

[sparky961]

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.

[SwarfnStuff]

Sparky,
    That is a new one to me. I have never heard of spade drills for metal, Wood n plastic yes but my little brain is struggling with using them in steel of any sort.
    Special type??????   

John B

[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]

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.

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

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

[vintageandclassicrepairs]

Hi All,
Going back to Will's original link,
In the video, the speaker says the the 3/4 drill has a split point
This would certainly help the drill to start without wobble, Although when used in a decent milling machine
the need for spotting or centre drilling is reduced

An interesting variation on drill sharpening is shown on one of Brian Block's videos where he demonstrates a "spiral point" drill grinder
https://www.youtube.com/watch?v=3unjoKkgQto

John
 

[sparky961]

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

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

I get 130 to 172 RPM, which sounds about right to me.

[AdeV]

Bugger, I forgot to convert feet into inches when I divided the SFM into the circumference. Blast these complicated mathematical thingmajigs! 

[sparky961]

Bugger, I forgot to convert feet into inches when I divided the SFM into the circumference. Blast these complicated mathematical thingmajigs! 

LOL... I cheated.  I used an app. ;)