Drilling through SS?

Tim R. · Apr 10, 2010

druid said:
Yup - used oil too. I just got a drill from KMS Tools - looks like that should do the trick for the last bit I have to do. I considered trying the other side, but it's convex and would be a b*tch to get started in the right place. I also thought of a smaller pilot hole, but when I thought of trying to drill through multiple times...

now, here's one I haven't screwed up yet: I need a stud for my 40-yr-old Volvo diesel. Dealer says it's no longer available, so I'm thinking of making one: get a SS bolt with the right thread for the one end, cut the other end to length, and thread it. So: any advice on threading a (approx) 1/4" SS bolt?

druid

You do not want to use a ss stud in an engine. It will be extremely difficult to cut the threads and it is just not necessary. Grade 5 steel should be used. Grade 8 is too brittle.

Ross · Apr 10, 2010

The end in the block is probably metric.

nick8489 · Apr 10, 2010

Tim R. said:
You do not want to use a ss stud in an engine. It will be extremely difficult to cut the threads and it is just not necessary. Grade 5 steel should be used. Grade 8 is too brittle.

Tim,
You've got me worried now as I have just replaced the bolts on the Water Pump and Alternator (the ones you have to loosen to make adjustments) on my Yanmar with SS ones. The originals have this built in washer arrangement and the heads are hard to get a spanner on. Are you intimating that there could be an issue with disssimilar metals? Or are you just saying SS is unnecessary?

jibes138 · Apr 11, 2010

Do not use diamond anything on ferrous metals. Ferrous metals are those containing iron like steels for instance. Diamond is pure carbon in a diamond arrangement structure of covalent bonds between the carbon atoms. So why not diamond? Carbon in soluble in iron. That is why you can make steel. By mixing carbon with the iron you get all kinds of different properties. What happens is at very high temperature (like those right at the cutting edge of your tool that is trying to shear the metal under extremely high concentrated stresses and high friction) the carbon atoms want to leave the diamong and diffuse into the Iron. The diamond will not last at all. For machining aluminum a diamond tool is miraculous and should last forever as carbon doesn't want to diffuse into the metal. A good example of carbon diffusion is how they case harden gear teeth by carburizing. In a high carbon furnace atmosphere the carbon diffuses into the iron and after quenching and tempering forms a very thick hard case for wear resistance. This same process happens at the tip of the diamond tool if used on steel.

jibes138 · Apr 11, 2010

depends on the grade of stainless but stainless bolts are probably a lot weaker than regular steel bolts. There are many grades of stainless some of which are martensitic and can be hardened and tempered making them a lot higher tensile strenght. Most stainless used for boats is not in this category as the martensitic stainless steels are not very stainless, they rust very easily. The grades used on a boat are austinitic and have a higher chromium and lower carbon percentage. The reason they are so hard to drill is they are typically around 20 percent chrome and chrome is a very hard material.
Another trick of the trade to consider in drilling. If you look at a standard hardware store drill then think of the speed right at the tip of the drill. The speed as you approach the exact center of rotation is zero. So at the center of the tool you are trying to broach the hole versus drilling it. The reason it takes so much force of penetration is to force the tip to keep moving through the workpiece. Someone mentioned a split point drill. The purpose of this is to not be cutting right at the center as there is no ability to cut right at the center, so you remove the center of the drill and push the cutting edge further out on the radus to where you are getting some relative motion. I once found a three fluted drill made by Guhring that actually had a hole in the center and as you drilled it created a little post and further up the drill the geometry was set up to break the little post off. These drills were fantastic. They would not wander off and held size beautifully. i was cutting through a forging die material and the hole was hardened on one side to HRc58 and the other side was about HRc40 as it intersected a bore that was case hardened. This was the only tool I found that worked. EDM was not an option due to recast layer.

sailingdog · Apr 11, 2010

One quick way to check is that the Martenisitic grades of stainless steel are magnetic, the Austenitic grades are not. Taking a magnet to the store to check the stainless quickly is a really good idea.

jibes138 said:
depends on the grade of stainless but stainless bolts are probably a lot weaker than regular steel bolts. There are many grades of stainless some of which are martensitic and can be hardened and tempered making them a lot higher tensile strenght. Most stainless used for boats is not in this category as the martensitic stainless steels are not very stainless, they rust very easily. The grades used on a boat are austinitic and have a higher chromium and lower carbon percentage. The reason they are so hard to drill is they are typically around 20 percent chrome and chrome is a very hard material.
Another trick of the trade to consider in drilling. If you look at a standard hardware store drill then think of the speed right at the tip of the drill. The speed as you approach the exact center of rotation is zero. So at the center of the tool you are trying to broach the hole versus drilling it. The reason it takes so much force of penetration is to force the tip to keep moving through the workpiece. Someone mentioned a split point drill. The purpose of this is to not be cutting right at the center as there is no ability to cut right at the center, so you remove the center of the drill and push the cutting edge further out on the radus to where you are getting some relative motion. I once found a three fluted drill made by Guhring that actually had a hole in the center and as you drilled it created a little post and further up the drill the geometry was set up to break the little post off. These drills were fantastic. They would not wander off and held size beautifully. i was cutting through a forging die material and the hole was hardened on one side to HRc58 and the other side was about HRc40 as it intersected a bore that was case hardened. This was the only tool I found that worked. EDM was not an option due to recast layer.

Tim R. · Apr 11, 2010

nick said:
Tim,
You've got me worried now as I have just replaced the bolts on the Water Pump and Alternator (the ones you have to loosen to make adjustments) on my Yanmar with SS ones. The originals have this built in washer arrangement and the heads are hard to get a spanner on. Are you intimating that there could be an issue with disssimilar metals? Or are you just saying SS is unnecessary?

Just saying SS is unnecessary to use as a stud in a cast iron block or manifold. Although I would imagine the expansion and contraction properties to be somewhat different.

RichBone · Apr 11, 2010

Donalex said:
Druid,
You don't say what you are trying to drill but is it possible to start from the other side? The opposite surface of the steel might not be work hardened yet.
Also a smaller pilot drill will allow the pressure you apply to be concentrated on a smaller point so improving the chances of penetration.
In any drilling operation one MUST see swarf coming from the drill immediately it begins to rotate and starting with a good sized centre punch dimple gives the drill a fighting chance. If at any time the drill stops making swarf stop immediately as the steel will harden in just two or three 'rubbing' - rather than cutting - revolutions.

Lastly, if you cannot get to the back of the piece I just wonder if one of those diamond powder coated drills used with water for tile drilling would help.
Anyone tried this as I am keen to learn if this is the way AFTER one has work hardened the workpiece?

Could you please clarify- swarf. I'm not familiar with that term.

Rich

txtowman · Apr 11, 2010

shavings swarf

Don12364 · Apr 12, 2010

Swarf is the chippings or turnings which come off the workpiece when drilling or turning it.
See:- http://en.wikipedia.org/wiki/Swarf.

Don12364 · Apr 12, 2010

Jibes

Hey Jibes,
Unlike myself, you were really paying attention in chemistry class - I can tell!
Not even under oil?

Thanks for the information.

BTW - Try telling my wife that diamond is only the 'see thru' version of whats left in our BBQ.

DougM · Apr 12, 2010

First of all, at least a Cobalt bit is necessary... High Speed Steel bits aren't going to work. Second, be sure the tip is cut at the proper angle for drilling metal, and that it is sharp. With the proper bit, stainless isn't that difficult to drill.

jibes138 · Apr 12, 2010

I agree with Doug...stainless is a pretty soft material but it is extremely ductile. When you cut it it is very hard to get the chips to break so when you drill you want to peck at it so the chips break and don't clog up the flutes of the drill that further prevents coolant from getting to the cutting zone. Ideally you want a drill that feeds the coolant under high pressure through two holes in the drill right to the cutting tip. Unfortunately you will need a very expensive non-portable machine for this. By the way feeds and speeds are based on the machinability of the metal and are usually given in surface feet per minute. The smaller the drill the faster the RPM since the relative speed is so much smaller where in the limit it goes to zero as the diameter approaches zero. So you need to run a small diameter drill at a lot faster RPM than a large diameter drill. Look up speeds and feeds and get the recommended speed for your application. You can't just accept some comment like..."run at 60 RPM" since it is totally dependent on the diameter of the drill and the material being cut.

jibes138 · Apr 12, 2010

A few other comments. A standard drill point is about 118 degrees included angle or the angle formed by the tip of the drill. From literature the recommended angle for 316 or 304 stainless is 135 degrees, so the drill point is a lot flatter than a standard hardware store drill. The other recommendation is the feed rate which has not really been discussed here and can't be controlled by hand anyway. The recommended feed rate is over .0015 inches per revolution. So you need to be moving this drill pretty fast through the workpiece. Let's say you are running at 200 RPM, you will drill through .300 inches of material in a minute. I assume the tubing you are cutting is less than a quarter inch thick? So it shouldn't take any more than a minute to drill a hole. Also you may want to try a solid carbide drill. It will be much harder and stay sharp a lot longer than a HSS or cobalt drill. A split point is also a must for this kind of work.

Sumner · Apr 12, 2010

Ok the easy way to drill stainless is with a plasma cutter

. If it isn't too thick I take the plasma cutter and try to center it on the hole and just hit it enough to poke a small hole through. Then I've had luck with the cheap nitrated HF bits, but I start as small as possible and move up about 1/32 nd at a time. Still faster to drill a 1/4 inch hole that way than trying to start with a 1/4 inch bit.

As has been mentioned you need a pilot hole as small as possible to start with if hand drilling and the plasma gives me that. If I'm off the mark a little I can adjust the hole by angling the drill as I increase the bit size.

When I use the mill or mill/drill I step up in drill sizes using about 5 bits to get from 3/16 to 1/2 inch even when drilling mild steel. A lot easier on my cheap bits and hey I'm retired

so I have time.

Druid if you still aren't having luck I'd try, never did it myself, but maybe take a small cone shaped grind stone in the drill and see if you can work through the area that is now work hardened by a few thousands and then try again with a much smaller bit and following some of the suggestions given by the guys.

Good luck,

Sum

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woodster · Apr 12, 2010

johnsons was company makes a drill fluid called TL-30 thats is made fore drilling ss and you can find it on line by doing a search ...it works very well ...just dip your bit in it and do so often ...it makes this type of drilling seem like drilling mild steel ....

regards

woody

Sam Salter · Apr 13, 2010

No one has mentioned this, but it's pretty easy to resharpen a drill bit, or even "flatten the angle"!
With a little practice you can get the clearance angles pretty good - any machine data reference will show the correct clearance angles - just guess them as close as you can and you can reuse the bit.
It's a bit of a dying art; I was taught during my apprenticeship; saves a lot of drill bits being thrown away or having to go down to the hardware store every time you break a drill bit.

sam

jibes138 · Apr 13, 2010

Sam Baby!!! Apprenticeship? What's that? I had a course with an old Swiss toolmaker. He sharpened all his tools for the lathe, including threading tools with a 60 degree included angle by eye. The guy was amazing. Unfortunately this country no longer values manufacturing or machining and is letting it all go overseas. It breaks my heart. I always sharpen my drill bits by hand and for wood and plastic they work fine, not sure I'd trust them on stainless but you make a great point. You can get a drill sharpener pretty inexpensively but would need to use drills a lot to make it worthwhile. More clutter for the garage, I need to get my wifes car out of there so I can have more space for my important stuff.