Drilling 316 stainless

I am making a small batch job of 25 items, the material is 22mm dia 316 stainless. For 12 of these items i use a 3mm HSS drill to drill through the 22mm dia, the drill lasted well i thought.

I have a small jig which my part go into which make the clearing of swarf not very good.

After my 3mm drill gave up i decided to look for something more long lasting, i found some TCT tipped drills supposedly designed for stainless. I use two drill to go less that half way through my stainless rod. I now have bits of carbice in a blind hole.

I have looked for 3mm diamond drills but they are pretty rare plus they need constant lubrication. Does anyone know of another type of drill i could use. I am using a pillar drill.

First option would be to sharpen your existing 3mm bit or just buy another the same and do the remaining 50% of the job.

Second is look at the quality of your HSS bit, is it a named brand, what sort of tip, any coating. I am moving over to the Dormer A002 bits which seem to work well - split point and Tin coated.

You could then go to one of the alloyed HHS and Cobalt bits which are harder wearing often refered to as HSCo, again Dormer do these and I have a few.

Solid Carbide will be better than the tipped drills which don't have that good a geometry for use in a pillar drill, they are a bit delecate but at least the tip should not come off.

Don't dother with diamond.

316 work hardens very easily. I suspect your drill speed is too high and the feed too low. This causes the drill to rub, which heats the steel, which hardens the steel which blunts the drill.

Use a slower speed, with a greater feed (ie. greater pressure to remove more metal per revolution), and don't forget lubrication.

also remember 22 mm /3 ..adds up to a very deep hole...

plastercine or putty dam and puddle of coolant...use oil for visability

woodpeck the hole..with draw drill completely every 1-2 mm at that size

like has been said keep cutting..low ish rpm and firm feed.

consider center drill or slot drill to get started [flat to start drill from].

its do able with hss..used to drill 4 1 mm holes 12 mm in 316s11 as a production part...

I make several items in quantity in 316. The secret is to BE BOLD. Speed a little less than normal, Feed very firm and keep it going, the drill, and any cutting edge needs to cut 316 not rub. PLENTY of cutting oil. If the drill is having a problem it will tell you by making a sound as though it has broken in the hole. Drill out, clear the swarf, add oil and plunge back in. This is the point where you must get the drill cutting as quick as possible, no need to ram it in just get push to get a cut going otherwise it will work harden. I use a 3.5mm drill for about 70 holes.

Definitely obtain some Cobalt drills, they will cut as normal. Had this problem a while back but the Cobalt drills did the job.

Clive

Push the drill, there should be two ribbons of swafe coming out, watch it,it's like a razor blade, handle it with pliers, after an inch or so appears, back the drill out of the hole, clear it, drill again, pleanty of coolant. I'v drilled 3" x 3/16" in 316 with HSS. Ian S C

Suggest you look at Cromwell Tools who list suitable drills for stainless from both Guhring and Swiss+Tech, with the 1060 range of ST ones having an offer price of only £2.90ea +VAT in the 2008 catalogue.

Regards

Trevor

I agree with all of the above, I work with machines built with 316 and we find that when drilling with a hand drill you need slow rpm but a lot of pressure, if you want to drill large holes then go up in stages to the finished size, I use rocol tapping compound when drilling and tapping also.

Martin P

Try these for drills. I use them for my job when required - http://www.drill-service.co.uk/

I would also recommend Dormer drills as above, however, not the tin coated type but the A100 series black jobber drills. Keep feed fairly high, speed low and plenty of oil (neat or soluble at around 8%).

Andy.

on a side note.... Watch on centre drilling or spot drilling. The 'lead' of these can burn the edges of the drills early and cause excessive wear before you've gone too far. What I'm saying is, just centre enough to stop the drill wandering on start.

Edited By M0BND on 23/08/2013 22:53:25

i also use ordinary dormer drills for stainless. i have some special 'strawberry jam' type cutting compound for stainless. no idea what the proper name is - always known it as strawberry jam!

i would endorse the previous comments about pushing the drill in and being more forceful than would otherwise be the case with other metals we use in model engineering. i would also endorse andy's comments as a usual centre/slocombe drill will work harden the stainless if allowed to go in too deep.

cheers,

julian

If you can, don't centre punch the start point, that spot will be work hardened. Ian S C

Thanks for all suggestions they will all be looked into.

I contacted the company that sold the TCT drill just saying they were worse than useless, they offered me replacment cobalt drills. so now waiting.

Like i said in my original post i am using a jig, i have since added a hardened drill bush. That make swarf clearance not to good though. I am using a bench pillar drill not a hand held drill.

Drill speed is lower that i would normall use for that size drill, i also use a steady continuous pressure releiving the drill every 30secs or so.

Will wait for cobalt drills and see how it goes.

For Stainless Steel I find "Rocol RTD cutting fluid" a must, it makes a world of differance, even with HSS drills

Edited By Dodweld on 24/08/2013 20:10:25

Edited By Dodweld on 24/08/2013 20:11:01

I saw a chap trying to drill through one of the HST Mk.3 carriage door handles to fit an accelerometer for testing purposes. Handles are investment cast stainless ANC20, hardened to Grade B. Drill wouldn't touch it, so he simple squirted some Rocol RTD on it and using the same drill, drilled straight through. Usual disclaimer.

> HST Mk.3 carriage door handles to fit an accelerometer for testing purposes.

So they could prove all the delays are down to the commuters not opening the doors fast enough?

Neil

<I wish my brane worked as fast as my typing fingers>

Edited By Stub Mandrel on 25/08/2013 17:21:28

Er no... it was a rather fascinating exercise. The Mk.3 carriage door handles are a lever type, as opposed to the dickie-bow version on Mk.1 & Mk.2 stock previously used. When the Mk.3s were first introduced, the handles started bending. It was down to the much higher rotational inertia of the lever handle; when the door is slammed, the direct rack-and-pinion drive imparted such acceleration that the 3/8" square spindle was twisting - it hadn't been a problem with the "balanced" dickie-bow jobs. It was first thought that hooligans were responsible! Anyway, some bright spark at the Railway Technical Centre in Derby came up with the ANC20 material - normally used for turbine blades - and it cured the problem.

Later, we were doing some work to improve the service life of the locks; we wanted to give them a 5 year life instead of the normal 3.1/2, so that the lock changes coincided with the vehicle "shopping". As part of the testing to prove the locks would last out, we needed to do a cycle test - but you can't ask someone to stand at a carriage doorway and slam it x thousand times - we needed a test rig. But how to calibrate the test rig to simulate actual real life slamming? Fit an accelerometer to the handle on the door, and then fit it to the test rig handle and adjust to suit.

So now you know...

Edited By Nigel Bennett on 26/08/2013 11:17:18

>boggle<

Neil