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Drilling holes in SS on Lathe

spurst

Aluminum
Joined
Aug 23, 2021
I am drilling holes in 304 SS 1/4 and one is 1/2 in. both are 1 in deep. I am having trouble with the holes being larger at the start side than the bottom. I have carbibe bits some with coolant holes some without i even bought a precise hole carbibe bit Cant get a a precise hole from top to bottom WHY. get just as good hole with a drug store bit as i do with a 200.00 carbide bit .
I have tried peck drilling, drilling slow, drilling fast, full retract no retract, center drill Drilling, with a Mori Seiki sl-2 tried a bit sleeve and a collet.
know i am on center in X What am I doing wrong.
 

cunaf85

Plastic
Joined
Mar 1, 2019
What does the tolerance look like? Do you face before drilling? Do you spot drill the part? Need to bore or ream the hole. You are calling it out in fractions, that usually means plus or minus 1/64, that isn't precision at all.
 

spurst

Aluminum
Joined
Aug 23, 2021
What does the tolerance look like? Do you face before drilling? Do you spot drill the part? Need to bore or ream the hole. You are calling it out in fractions, that usually means plus or minus 1/64, that isn't precision at all.

Yea I need the holes to less than .0005 Drilling them lucky if the hole is within .003 allways cone shape larger toward the turret. Yes i face the rod then center drill or spot drill makes no differance. I press them to a shaft force fit,
 

DanASM

Hot Rolled
Joined
Mar 11, 2019
If i need a .250 and .500 hole within .0005 what size do i drill before ream, how much will a reamer take off and stay accurate. Thanks for your help

I am using a .242 ("C") Drill for a .2505" Reamer in 303 SS right now.

If I was drilling a .500" hole I would use .4844" (31/64) Drill, with a carbide tipped reamer.
https://www.mscdirect.com/product/details/72190325 Example.

Generally you want to use at least .008" undersized drill for smaller reamers up to .020" for larger ones. Once over half inch I think boring becomes cheaper and easier.
 

jspivey

Aluminum
Joined
Nov 18, 2018
Location
Southern Illinois
Leave roughly 2%-3% of the diameter of the finished hole. So for 3% of the .500" hole, you would leave .500"*.03 = .015". If you will be purchasing a reamer for this, go by the manufacturers recommended speeds and feeds.
 

MaxPrairie

Hot Rolled
Joined
Jul 9, 2015
I am using a .242 ("C") Drill for a .2505" Reamer in 303 SS right now.

If I was drilling a .500" hole I would use .4844" (31/64) Drill, with a carbide tipped reamer.
https://www.mscdirect.com/product/details/72190325 Example.

Generally you want to use at least .008" undersized drill for smaller reamers up to .020" for larger ones. Once over half inch I think boring becomes cheaper and easier.

Yesssssss......(need at least 10 characterssss)
 

DanASM

Hot Rolled
Joined
Mar 11, 2019
Yesssssss......(need at least 10 characterssss)

I use brown and sharpe screw machines. I have to use HSS tools and sometimes carbide on the O.D.

I have been running 3k-5k collars at a time with TiN coated Cobalt drills and a carbide tipped reamer like I referred to above. I tool these jobs up and run them until complete without touching anything. Last parts look pretty close to the first parts. This is in 303 SS.

In 304 you will want to make sure the reamer is taking a chip to avoid work hardening. Trial and error though. I would use the numbers I gave you in 304 and see what happens. It will probably work fine.

Good luck
 

Zeuserdoo

Aluminum
Joined
Aug 31, 2015
Location
The Moridor
If you need the holes to be within .0005, no drill is going to do it. Either drill and ream or drill and bore.

I can get drilled holes all within .0005 the time. I use a coolant thru double margin drill and make sure the drill is on dead center X & Y, and they usually only oversize by .0001-.0003.
 

MaxPrairie

Hot Rolled
Joined
Jul 9, 2015
I had a guy come by my shop a couple years ago and wanted a pretty simple part made. I did it and he paid me in yg dream drills. I told him he way overpaid me but they all came from where he used to work. As soon as they started drilling half a thou oversize they switched them out. Most were basically new. Sent about 20 out to be resharpened. They had buckets of these things and were throwing them away until they figured out scrap carbide is worth something.
 

guythatbrews

Cast Iron
Joined
Dec 14, 2017
Location
MO, USA
I can get drilled holes all within .0005 the time. I use a coolant thru double margin drill and make sure the drill is on dead center X & Y, and they usually only oversize by .0001-.0003.

I dont have to hold that close but use a bunch of this type of drill. CNC screw machine neat oil hi pressure coolant. Usually can't get an on size gage pin to go in the hole or maybe just start. These drills work very well and last forever in austenitic SS.

What brand drill are you using and arer they intended for 304SS? You don't mention a depth but if it's not too deep I would bore it if you are having trouble. You will likely have trouble with the reamer too if you have the proper drill and it's not drilling well. Maybe really check alignment and axis motion. Have you checked a gage pin in the collet?

I had some ER16 holders that worked fine for anything under 10mm but they ran out like a bitcth at 10mm. Turns out the clearance hole behind the collet taper was eccentric and was forcing the shank out of line.
 

CITIZEN F16

Titanium
Joined
May 2, 2021
Have you checked to make sure the drill is aligned and then a reamer? Big in the front points to a drill that is not on center.
 

CITIZEN F16

Titanium
Joined
May 2, 2021
I had a guy come by my shop a couple years ago and wanted a pretty simple part made. I did it and he paid me in yg dream drills. I told him he way overpaid me but they all came from where he used to work. As soon as they started drilling half a thou oversize they switched them out. Most were basically new. Sent about 20 out to be resharpened. They had buckets of these things and were throwing them away until they figured out scrap carbide is worth something.

A long time ago the tool crib attendant only wanted the carbide tooling back to exchange for new, even though everything was signed out with your employee number. We only resharpened the boring bars we used in our department everything else got tossed. It was a pretty good sized facility with only one tool crib. I wish I knew now what I didn't know then. None of the 8 shops I worked at recycled the carbide, except obviously that tool crib attendant.
I bet that new 4 wheel drive Bronco he had was paid for by the scrap he walked out with that no one cared about.
 








 
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