Drilling Stainless Steel

[BCR751]

[Two duplicate threads were merged into this thread.  First two posts are redundant.  -the management.]

I need to drill some small holes in a piece of stainless steel.   Drill size is #72.  I tried the regular bit set from Micro Mark.   They wouldnt even start.  Is there way to make these work or
do I need to get some carbide bits?

Doug

[peteski]

Not sure why you posted this question specifically in the H0 and Large Scale section.

Yes, carbide drill  (PC board bit with 1/8" shank) bit will easily drill through carbide. Those bits are very fragile - best to use them in a drill press. And make sure to have some good backing material or the drill will shatter when it comes through the stainless steel. Piece of brass or aluminum would work well.

[BCR751]

I need to drill some small holes using a #72 bit into a piece of stainless steel.  I tried using regular bits from a MicroMark set but they wouldn't even start.  Is there a way to use these or will I need to purchase some carbide bits?

Doug

[peteski]

I guess I'll also duplicate my answer here. 

Yes, carbide drill  (PC board bit with 1/8" shank) bit will easily drill through carbide. Those bits are very fragile - best to use them in a drill press. And make sure to have some good backing material or the drill will shatter when it comes through the stainless steel. Piece of brass or aluminum would work well.

I've bought some from  https://drillcity.stores.yahoo.net/ , but you will likely also find them on eBay and Amazon (but the prices might be all over the place).

[Chris333]

Drilling stainless just sucks and when it stops cutting and starts heating up it becomes more and more harder to drill.

[MK]

Do you need to use cutting fluid or lube oil?

[Chris333]

Use slowest speed.

I've heard to use water to lubricate. 

[peteski]

As I understand it, drilling likely causes work hardening. See https://en.wikipedia.org/wiki/Work_hardening and https://www.harveyperformance.com/in-the-loupe/avoid-work-hardening/. Plus, the material is likely already quite hard.

Carbide drills only cost few bucks a piece (or even less), and will drill through this stuff easily.  Lubrication will be helpful, but it is not like we are drilling a large hole. This is only 0.026" or 0.66mm hole.

[Chris333]

That is what I meant by it just gets harder... literally. So when you run the drill full speed and it starts burning the metal is getting harder the more you go at it.

[narrowminded]

Also, in case you're doing it, avoid center punching SS.  That work hardens the exact point where you are drilling and it's pretty dramatic.  I used to demonstrate that to new shop folks by having them take a scrap piece of SS (1/8"?) and center punch for a small hole (1/8"?) and then drill it in the drill press.  Then, immediately next to it, drill again but without the center punch.  It's dramatic and the operator can feel it.  I'd also have them vary the degree that they "centerpunched" the material, really whacking it or angling and then whacking again to move the center, as they might do in aluminum or steel to be sure they "got it", a big dimple, and then a slight light "prick" just to help pick up the center.  Amazing difference.  This is useful, practical knowledge for anybody working with tools to understand and is easy to demonstrate to yourself with a drill press and a scrap piece of SS. 

Other commonly used metals we encounter, brass (it's especially the copper in it) and aluminum are a couple, are affected this way but it's nowhere near as dramatic when machining and can actually improve machining characteristics, improving the natural "gummy" machining characteristic of some of those materials.  That article that @peteski linked to explains the science behind this in better detail but for the shop guy it's useful to know that of all of the materials he will encounter, avoid deformations in SS anywhere that you'll want to machine it.

Another example of work hardening or "cold forging" is to bend and then straighten a paper clip.  It will never get back to perfect with a retained bump right at the point of the bend.  That's the work hardening effect.  In a way, it's the same reason that some parts are "forged" instead of cast.  They work harden in the distorted area, developing a grain much as wood has.  That can be desirable and done on purpose, such as forging steel.  Side rods on many steam locomotives were hammer forged to take advantage of this characteristic, another related thing that could be researched for a better understanding.  Also, an explanation of the difference between cold rolled (work hardened) and hot rolled steel of the same grade/ makeup (use 1018 as an example) demonstrate the work hardened effect in real numbers.  It is very real.

 

[Steveruger45]

Yep, all of the previous.
When I drill SS I use a carbide bit, slow drill speed, frequent release of cutting pressure during the drilling process, avoid center punch before drilling and a use a cooling cutting fluid or light oil.  In short, let the drill do the work, don’t force it.  If drilling straight through use a backing plate of a softer metal.  The latter is a good idea anyway no matter what your drilling through.

[BCR751]

Not sure why you posted this question specifically in the H0 and Large Scale section.

Because my mouse seemed to have a mind of its own for a moment and I clicked on the wrong section.  And, I tried to delete it from that section and couldn't for some reason.  My sincere apologies.

I've ordered carbide bits from drill bit city before.  I would have tried that if I had the correct size for this project.  I'll give Paul a call today and order a few of the #74's plus some others I have broken .

Also, what speed is slow enough?  I'm able to change the speed on my drill press by rearranging the drive belt.  Should I go with the slowest speed possible and use cutting fluid?

Doug

[Steveruger45]

Also, what speed is slow enough?  I'm able to change the speed on my drill press by rearranging the drive belt.  Should I go with the slowest speed possible and use cutting fluid?

Doug

Hi Doug,
Use the slowest speed your drill press will do.  Once you have that set proceed to drill with little pressure, that is just enough to cut and then release the drill contact with the metal frequently as you go. Adding cooling/cutting fluid as you go.   What you’re trying to do is keep the heat generated down and keep the drill bit actually cutting the metal when it is in contact and not just spinning and generating heat.

In a way it’s like trying to describe how to start a car with a crank handle, yes I still remember those days, it’s easier to understand the technique by doing it. Although there is science involved the technique is more of an art.
Hope this helps.

[CRL]

I was in a machine shop years ago watching them drill a 1.5” hole in a 1/2” SS plate. The drill was making about one revolution per second (60 rpm) and was under constant pressure and a stream of coolant. The machinist told me if they allowed the drill to spin with no pressure, it would ruin the cutting edge. Very interesting to watch, but impossible to pull off without a very specialized drill press.

[Steveruger45]

Yes CRL.  In a pro workshop and on a large diameter hole that size that’s the way to do it.
Yes you want the drill when in contact to cut all the time but that is a function of drill speed and hole size.
I doubt a drill press most of us have at home can actually go that slow though, plus the size of the hole to drill in this case is immensely smaller, so just suggesting a doable work around with what we all probably have at hand.