Drilling 316 Stainless Question - Small Hole - Tiny Bit!!!! = Breaking

[the.hogman]

I am having a heck of a time. I am having to drill press 1.15mm (.0453") holes clear through 3/16" SS 316 round. According to charts I am calculating about:
(45 SFM x 12) \ (.0453 x pi 3.14) = RPM 3,600 with a feed of .001"

Does this make sense? I have never worked with stainless before and this seems like the RPM is so high it just asks for rubbing and work hardening. I "common sensed" it and run about half that speed, but it really doesn't seem to matter. Additionally, I am center punching. I am sure this doesn't help either.

I am using HSS oxide 118 degree bits. Whether I use coated or not, I am breaking every bit I have in stock.

I have a very solid steel work piece jig so rigidity is not a big factor right now.

HELP! Do I go cobalt, 135 degree split point bits? I really appreciate all of the knowledge on here. I am open to any suggestions.

 

[chevydyl]

Whenever I drill stainless peck it, when using a hand drill I would pump the trigger and push as hard as the bit would allow, use coolant, not oil, and yeah I think I would slow it waaaay down doing light pecks, might take a bit of time but it may work.

 

[brino]

Hi Hogman,

Small problems that would not matter for larger drill bits, could certainly cause problems here.
Have you checked the run-out on the drill press chuck?
Lock the table, stick a magnetic base to it and indicate a known straight rod held in the chuck, turning by hand.
Small bits can't take too much run-out, it looks like constant side pressures on the bit.

Please post back with what helps and what doesn't.

-brino

 

[BobSchu]

Use cobalt bits, very slow speeds, and lots of pressure. 3600 RPM is way too fast for stainless, especially 316. I've never really needed coolant or lube if I used these methods. I drill lots of stainless at high tech facilities and kitchen installs and they usually use 316 or 304 grade stainless for most of the equipment.

Bob

 

[Wreck™Wreck]

What kind of machine are you doing this with? Insufficient feed rate will cause problems but a feed rate that is not well controlled is even worse.
3600 RPM seems a bit slow, also program the feed to peck one or two diameters on the first peck and no more than one diameter on subsequent pecks then even less if the hole is multiple diameters deep. Start with a spotting drill which will deburr the hole as well.

Good Luck

 

[brino]

Your getting some varied feed back on speeds.....

One other thing that might help is a sensitive drill press or adapter like these:
(So you can feel as well as hear and see what's going on.)

http://www.ebay.com/itm/Dumore-Mode...nWIXPRUOe1q7fGG%2FdK4%3D&orig_cvip=true&rt=nc

http://www.lighttoolsupply.com/catalog/Product/Micro-Drill-Adapters?productID=338424

Although you may not want to dedicate a machine to small drilling, the adapter seems reasonable if you are going to be doing much of this.


-brino

 

[chips&more]

I know what the speed chart says. But in my home shop, I do not have a speed chart anywhere to be found! A home shop is typically just that, what the home owner has acquired and a finesse to use them. If I was to drill a 0.0453” hole in 316 stainless in my shop. I would first start and try the spindle speed around 500 rpm and with a good lubricant and feel the feed. Note; to feel the feed would require a sensitive drill press or the like. You can of course increase the spindle speed as you find the sweet spot. As for what type of drill bit. I guess a Cobalt spilt point would work well. But a standard HSS should also work. And a Carbide drill bit (like the circuit board ones) would be a great choice, but rigidity and other factors are really important, or you will break the Carbide drill bits like dropping glass. I do a lot of micro machining and a 0.0453” drill bit is actually quite large for the typical work I do…Good Luck, Dave.

 

[JimDawson]

As you know 316 SS work hardens if you look at it wrong, so you have to keep enough pressure on the bit to keep it cutting rather than rubbing. I'm thinking the speed chart or calculation would be about correct under ideal conditions. Having said that, I would turn slower and feed with all the pressure the drill bit will take. Peck drill, but be aggressive with the feed. A 135 degree cobalt bit would be my choice for this operation. For larger diameters (> 0.100) I might go with carbide, but using a manual machine the flexibility of a cobalt bit might be helpful to minimize breakage.

 

[Doubleeboy]

When I want to make sure a drill bit starts drilling quickly and not rub first, I hone the cutting edge of the drill with a diamond stone, getting the edge just a little sharper helps it get a bite and start working quicker, instead of rubbing. Like Jim said, once it starts cutting be as heavy on the feed as you can without bending or breaking the drill. For small holes I like Tap Magic cutting fluid, either the current stuff or better yet the old stuff with TCE in it.

michael

 

[the.hogman]

All great comments and thoughts. I found out several things last night. No wonder it can't drill these holes!!
First, There was vibration due to a lump on the old drive belt, not great, it was passing down to the bit.
Second, there was almost ZERO runout on the chuck, good.
Third, the spindle as it extends get extremely sloppy. BAD! enough said here....
Fourth, the press can't accommodate the "required" RPM. not great, but workable with finesse.

I disassembled the press and found that the body casting could not be split at the spindle to put in a pinch bolt and the clearances were too small to put in a bushing, the two best options. Knowing the drill press is essentially worn out, I drilled, tapped and put four screws with brass tips around the spindle casting (and tightened the alignment grub) to take away any lateral movements. Of course this made it stiffer to go up and down, but it was much better with little movement at extension.

Long story short, the press will be heading to the metal scrap bin later. I have a Dumore high speed precision drill press on the way and have begun a search for a high quality floor drill press. This will hopefully put an end to this misery... I sure do enjoy reading all of the helpful suggestions and comments. Thanks!!

Below is what I make out of 360 Brass. I am now making them out of 316 stainless (with these God-forsaken holes for the hinge pins). Banjo and guitar capos. I hand make every piece of them myself, including the knurled thumbscrews.