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Different Countersink Bits

04/20/2016 8:56 AM

Could some of you master machinists please explain to me the different uses, or pros & cons of the two major types of countersink bits? My guys are using bits like the 3rd from the left, and they are breaking constantly. The material is a stamped stainless steel part, 1/4" thick. Years ago when I was a machinist, I used both styles, but never really knew why one was chosen over the other. The obvious choice to me is to use the other type to stop the chipping of the tool. Suggestions? Thank you for your assistance.

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#1

Re: Different Countersink Bits

04/20/2016 9:19 AM

I've never used the third from the left type. Only one cutting surface as opposed to 3, 4 5 or 6 cutters seems a no brainer to me.

Could be a de-burring tool instead of a countersink tool, but that's a guess.

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#22
In reply to #1

Re: Different Countersink Bits

04/21/2016 2:50 AM

The multi cutting countersink device in some cases and with different materials leave an uneven, not nice looking surface.

This will not happen with the one-hole de-burr countersink bit. So I was taught during my machinist training time at first to drill the final diameter of the countersink hole with a standard drill bit to remove most of the material in the countersink area and then cleaning out the excess material (drill bit tip angle to 45deg. of the countersink) with the one-hole countersink. These were available for the common screw sizes. Really nice countersinks!

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#2

Re: Different Countersink Bits

04/20/2016 9:21 AM

"These tools are best used as deburring tools, where the burr from a previous machining operation needs to be removed for cosmetic and safety reasons, however they may be used in softer materials (such as wood or plastic) to create a countersunk hole for a screw."

https://en.wikipedia.org/wiki/Countersink

preferred...

Link...

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#10
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Re: Different Countersink Bits

04/20/2016 12:08 PM

Thank you Solar, that pretty much answers my question.

Thank you all for your input!

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#3

Re: Different Countersink Bits

04/20/2016 9:32 AM

The third type of countersink is known as a cross-hole countersink cutter. Wikipedia claims that this type is best for deburring. In other words, these should be used just for removing a tiny amount of material and leaving a clean surface. Significant excavation should then use a fluted countersink used at the proper speed.

If your guys are breaking and not just dulling either of these tools then either the CNC programming or your guys capabilities need some realignment.

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#4
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Re: Different Countersink Bits

04/20/2016 10:20 AM

Speed and feed.

If these guys are breaking tools, they aren't machinists, they are handle turners.

I've been using machine tools for 50 years and while I've broken small twist drills, I've never broken a countersink tool.

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#6
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Re: Different Countersink Bits

04/20/2016 11:21 AM

I like the expression, "handle turners". A lot of learning goes into machining. I never cease to be amazed at the craftsmanship put out by the old machinists at my plant. A lot of people will see chunks of metal while I see works of art.

I guess those who really appreciate good machining have probably tried to do some themselves. Everyone else has no idea.

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#38
In reply to #6

Re: Different Countersink Bits

04/21/2016 10:26 AM

Yeah, the formulas tell you what 'should' happen under 'nominal' conditions, but is the steel your cutting into actually the steel you think it is, all the way through, or is there a 'pocket' of higher-than-nominal nickel content that's going to overheat the drill if you continue as 'the book' says. Metalwork is as much an art as Woodworking; the 'grain' on metal may be much finer, but it's there, in how the crystals have formed as the metal cooled. You need to 'read' the piece as you're working with it, just like carving a duck from wood, or carving an elephant from granite. ("All you do is cut/chip away whatever does not look like a duck/elephant," as the old saying goes.)

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#33
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Re: Different Countersink Bits

04/21/2016 9:32 AM

Truer words never said about "machinists". With all the CNC capabilities these days, most are just machine operators relying on the programming. A true machinist probably would not ask for a countersink bit, but resharpen a regular drill bit from the normal 118° or 135° most common point angles, depending on the number of countersinks to be done and the angle of countersink required. But, machinists these days are a rare breed. Not too many left who can talk the terminology of the actual tools and what each affects in terms of performance.

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#42
In reply to #33

Re: Different Countersink Bits

04/21/2016 2:22 PM

Actually, this only works if 'real' countersinks aren't available. The 90 degree flutes tend to create chatter which requires lowering the SFPM, sometimes accomplished by turning off the machine and 'coasting' to a stop. Only doable for a few parts, not production. (remove the tool before your torque gets too high) Odd number of flutes generally work best (except 1), but it depends on material and other factors.

Countersinks can be speed and load sensitive at times; you may need to adjust quite a bit from suggested RPM and/or feed-rate.

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#5

Re: Different Countersink Bits

04/20/2016 10:32 AM

1) They are definitely using the wrong tool, and are abusing it while they are misusing it.

2) If they had the correct tool, they would need to slow down the rotation rate, and reduce feed rate to match the cutting with the material. They also need to use the correct cutting fluid to reduce heat shock to the tool. The one on the upper right seems like an appropriate tool to use for the task at hand, as long as the hardness of the tool is way above the hardness of the particular stainless steel.

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#7

Re: Different Countersink Bits

04/20/2016 11:30 AM

FYI... this is being used on a basic manual drill press. Simply c'sinking a drilled hole. Not a CNC, and not even an automatic feed drill. Just a hand operated drill press with a lever and an adjustable stop.

It's embarrassing that I even have to personally address such a basic operation out on the floor, but it is what it is. In their defense, most of these guys are press/stamping plant kind of guys; not traditional "machinists". But it's still basic stuff. So, yes, I'm disappointed.

But in order to fully explain things, I needed more info on the cross hole countersink, that I could relay to them. It's a teaching moment.

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#8
In reply to #7

Re: Different Countersink Bits

04/20/2016 11:43 AM

Just tell them it is a DE-BURRING tool and not a countersink tool.

Countersink tools are a specific taper, depending on the screw used.

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#9
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Re: Different Countersink Bits

04/20/2016 11:50 AM

Right. Well, the bit we have is actually an 82 degree tool, so it works as far as fitting the print. It's just a matter of someone not understanding tools and ordering the wrong tool for the job, at some point during the process sheet being put together.

This kind of thing is the reason I do a daily walk or two through the whole shop, to find things that otherwise would never be brought to my attention.

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#11
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Re: Different Countersink Bits

04/20/2016 12:33 PM

I would also suggest some cutting oil and low RPM range....

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#12
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Re: Different Countersink Bits

04/20/2016 12:58 PM

Nice old photo, even if she (the operator not the drill press) is cutting 2" holes in wooden planks.

I wonder what they are making? Outhouse seats (1-holers) for midgets?

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#13
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Re: Different Countersink Bits

04/20/2016 1:23 PM

She is making parts for wooden reels used for winding barbed wire.

A plentiful byproduct is wood chips.

Britain, circa 1917.

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#14
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Re: Different Countersink Bits

04/20/2016 1:24 PM

Wooden spools for barbed wire circa 1917.....

1901.... Heinz factory worker labeling ketchup bottles...

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#21
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Re: Different Countersink Bits

04/21/2016 1:19 AM

Most countersinks used are either 60o and the 82o. The 60o is most often used for placing a tapered hole in a piece of metal that will be rotated on a lathe. This is placed on the other end from the chuck (usually the right end) so that a live center can be used to hold the end that is not chucked. Most live centers are used for metal or large diameter wood or long lengths of wood on a wood lathe to prevent wobble.

The 82o countersink is normally used for making the tapered underside of the most common type of flat head screw/bolt. Most often but not always. In a machine shop almost anything will be tried to get the job done.

Good Luck, Old Salt

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#34
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Re: Different Countersink Bits

04/21/2016 9:38 AM

Lyn pointed out speed and feed. If you are going to have a learning moment, have someone teach them that you just cannot lean down on the handle of the drill press as most people do. It is an art after all. I have had to teach my guys how to do it and I have a lot less breakage of cutting tools these days.

I am sure you can look up speed/feed charts on line, or in Machinery's Handbook or other reference materials. Make a chart and post it.

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#35
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Re: Different Countersink Bits

04/21/2016 9:43 AM

Well, I can look up speeds. But looking up feeds isn't going to do me much good on a manual drill press where someone is pulling down on a handle to form merely a countersink. Unless I put one of my cyborgs on this job. I think I can program a feed rate into his right arm

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#37
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Re: Different Countersink Bits

04/21/2016 10:24 AM

This is more about getting a good feel for the way the bit is cutting, not something you can programme.

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#41
In reply to #35

Re: Different Countersink Bits

04/21/2016 11:09 AM

Consider using a mechanical weighting system for the drill press handle? Would that be more reproducible? I don't know.

Whatever you do, before you do that, make sure the work is rigidly fixed at the drill press table, so that the tool does not move the entire work around in some odd orbit.

Then tell the operator to only apply sufficient pressure to get a single curly swarf (chip) production while cutting. If they cannot get to that point, you need to go back to the drawing board on the tool itself, and re-examine the set up.

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#15

Re: Different Countersink Bits

04/20/2016 1:37 PM

If you are countersinking for a flat head screw, I would assume an #10 or smaller, in stainless steel I would go with a multi-flute style countersink ( 4 or 6 flutes). If the hole that is counter sunk was stamped, the stainless steel will be work hardened around the hole, and this is what is causing the chipping of the tool cutting edge.

The one thing with a multi-flute c-sink, you need a slow speed and a heavy feed to keep the tool from chattering.

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#17
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Re: Different Countersink Bits

04/20/2016 2:46 PM

Could some stamping operation be produced such that the hole is formed and countersunk simultaneously without vastly distorting the sheet of stainless steel? It would seem not. If the material was work hardened, this means even slower cutting speeds, perhaps a change to a carbide material (probably not most of the high speed steels as per normal). Maybe this means a complete change in tool.

Maybe they will need a rig-mounted die grinder to countersink such hardened material. Then at least, they would be replacing something other than bits (such as grinding rocks).

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#16

Re: Different Countersink Bits

04/20/2016 1:44 PM

I prefer to use the cross hole bit. I find that the multi-flute type can be prone to chatter leaving a rough surface. The cross hole does cut a little slower so perhaps your guys are leaning on it to try to speed it up. With this type, all that does is to increase the friction & therefore the heat. If you have a decent quality bit it is quite capable of countersinking as well as de-burring.

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#20
In reply to #16

Re: Different Countersink Bits

04/21/2016 1:18 AM

Hi All

For my own information, do countersinks with an odd number of teeth tend to chatter less?

Tony

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#30
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Re: Different Countersink Bits

04/21/2016 8:47 AM

No chattering at all if the shop is kept above about 5 C.

Multi-fluted countersinks with odd numbers might be better than even numbers, but none of them chatter when weight on bit is maintained at a high standard amount, and bit speed is kept low. Then the material removal should be more or less a continuous chip, rather than lots of really short tiny ones, where the bit is "bouncing" up and down onto the work. If bit heating is an issue, then they need to slow down the bit, and use raising and lowering of the bit several times to get a smoother countersink.

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#18

Re: Different Countersink Bits

04/20/2016 11:37 PM

You need to describe what the "burr" is from and how it looks. Are you using a hand held drill, or a drill press or some other secondary operation machine? If it is a drilled hole, and the bottom side has an irregular burr caused by a twist drill poking through, that is a different problem from a clean punched hole with a sharp corner. I don't like those multi flute bits on any hard materials as they chatter and don't leave a smooth chamfer especially with a multi flute. The single flute of the type you showing are good, but they don't last for long on stainless as most of them are high speed steel, get a cobalt bit if you can find one. I like the more common single flute bits, the ones that look like a stubby single flute twist drill, 90 degrees for a chamfer usually works. They are easy to resharpen also if you have a "machinist" handy. If you are "chipping" the bits you are probably over speeding it, stainless steel with a proper chamfer bit will cut all day long at 100-250 rpm, slower is faster with stainless steel. If you are using a drill press or mill for the debarring a carbide bit at proper speed will last for thousands of holes.

If it is a clean punched hole and you just want to take the "curse" of of it you can use a stainless or non woven wheel.

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#19
In reply to #18

Re: Different Countersink Bits

04/20/2016 11:47 PM

Stamped SS part.

Manual drill press with non-machinist operators.

Countersinking for screws.

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#36
In reply to #19

Re: Different Countersink Bits

04/21/2016 10:01 AM

Stainless steel is more ductile than regular steel, and also work hardens as a chip is removed. The multi flute cutters want to take off lots of small chips and will chatter causing more work hardening. You want a fairly aggressive cut at low speed, so look for a uniflute type of countersink, a carbide one will work ok in a drill press, cobalt is ok, hs steel not so much. Get the drill press going at it's slowest speed (100-250 rpm tops, slower is better) so the chip peels off with constant pressure. A little cutting oil goes a long way with stainless steel which wants to weld to the cutting edge, nitride or other coatings for stainless are available. Put a small fan on the operator or fume extraction because it will get smokey from heat generated! Try to get to a spiral chip( cutting), not lots of little chips (grinding work hardening) with your feed rate.

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#23

Re: Different Countersink Bits

04/21/2016 4:00 AM

The cross hole bit works fine if used properly.

If you are removing the burr left from stamping in stainless steel I suspect there is some work hardening of the burr. To cut stainless the cut must be firm and consistent other wise it aggravates the work hardening of the material this will certainly destroy your countersink if you persevere.

I suspect your workers are doing the job with a loose work piece, this sort of countersink will not handle the job well unless the work piece is clamped so that the cut is consistent and not wobbling around,I know it slows the job down but it is the only way to get consistent results.

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#25
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Re: Different Countersink Bits

04/21/2016 6:24 AM

That's correct garth, the piece is loose; hand-held. Approaching stamped hole from non-burr side. A couple thousand (ring shaped) SS pieces at a time, with two holes per piece, so part must be spun around to hit second hole (the jig does have a central hub for alignment). Clamping for a c'sink could be cost/time prohibitive. An alternative would be preferred. 82 degree bit for flat head screw. The c'sink is only about 5/32 deep. Cutting fluid is being applied.

So I have heard suggestions of:

Cross-hole with a lighter touch

Cross-hole with firm pressure

Multi-flute (warned of excessive chatter)

Single flute at 100-250 RPM

Doesn't seem to be a consensus.

If I were to go with a standard bit (not the cross-hole), is there a flute number that would work best in these circumstances? Single flute, 2 flute, 5 or 6 flute, etc? Is there a disadvantage to the higher flute bits? Generally speaking, is there a different speed recommended when using a single flute as opposed to using a 5 flute?

Because of the way it's made, the standard type bit has a hardier cutting edge than a cross hole. What am I giving up by using a standard bit instead of a cross hole? These are the finer details that I never had chance to learn during my 3 years as a machinist, many years ago. And unfortunately, I currently don't have any wizened old true machinists amongst my employees. Mostly press men, and mostly young.

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#26
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Re: Different Countersink Bits

04/21/2016 6:43 AM

Single flute, like these, slow speed, firm pressure but not too firm to give work hardening, plenty of cutting fluid.

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#27
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Re: Different Countersink Bits

04/21/2016 8:21 AM

Thank you Nigh.

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#46
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Re: Different Countersink Bits

04/21/2016 9:08 PM

I have been using the cross hole type of countersink ( yes it is sold as a countersink, i disagree with Wiki ) in SS for a good number of years. Countersinking holes up to 12mm diameter. I don't like the multiflute as they chatter when hand holding the drill and/or work and so i won't use one. If they made one with the teeth spaced unevenly (not just odd ) i would try one. The cross hole WILL move off centre if not held straight with the work aligned. This type has been made to eliminate this.

http://dewitt-tool.com/csinks_weldon82d.aspx

Unlike most others i DO NOT use coolant. It is slippery and allows the tool to turn without cutting. This immediately hardens the surface. GARTH has said that you need to keep the tool cutting and i concur. You need to start soft ( because it is a thin edge ) and gradually increase pressure as the cut gets wider. I used to teach my staff by getting them to place their hand on the handle of the drill without pushing. I put my hand on top of theirs and pushed down at the correct rate and they could feel me increase pressure through the cut.

Because you are not using coolant/lubricant you need to go slow, very slow, very very slow, about 50rpm I have successfully used cheap knock offs in SS by this technique but they don't last long. The brand in the link is good.

REMEMBER start soft, end hard. Kind of wrong, eh?

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#48
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Re: Different Countersink Bits

04/22/2016 4:00 AM

I like the piloted c'sk although you would need one dedicated to each hole size. Shame they don't seem to do a 90° bit to suit ISO screws.

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#50
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Re: Different Countersink Bits

04/22/2016 9:08 AM

Thank you for the link. That is always good to gain another resource for tooling.

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#39
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Re: Different Countersink Bits

04/21/2016 10:49 AM

Single flute tool would work best. The idea is to try for a single continuous chip this reduces the possibility of work hardened material remaining which will cause the cutter to bounce rather than cut, from that point on is a descent into hell.

Most important is fixed position of work piece, if your cutter starts to move the job around you will loose the consistency of the cut of the chip, single flute tools tend to deflect the work piece so give this serious consideration.

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#40
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Re: Different Countersink Bits

04/21/2016 11:05 AM

You really got a tight focus on the situation with this last reply:

"Most important is fixed position of work piece,..."

Rigidity, lubrication, and speed are key, and they apply not only to the tool, but the work piece as well, so whatever they are doing now to secure the work at the drill press table is probably no where near adequate for good results.

Any precision drilling, reaming, counter boring, etc, must always have things held tightly in place, or the results take on odd sizes and shapes.

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#24

Re: Different Countersink Bits

04/21/2016 4:55 AM

Are they using the cs dry? The drag on the back area will be very high if not lubricated with cutting oil/coolant.

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#28

Re: Different Countersink Bits

04/21/2016 8:24 AM

I think I'll go with the one on the right, in HSS.

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#31
In reply to #28

Re: Different Countersink Bits

04/21/2016 8:56 AM

You would be better served with the TiN coated one, since the cutting surface is much harder and will stay sharp far longer on such hard materials as stainless steel. Slow down the countersink rotation speed! Much slower than you would use for carbon steel.

Remember that hole punch hardens the material around the hole, that is a fact, just as hammering will harden copper. This last choice you made to go with an actual countersink tool will be much better result than De-burring tool you have been using.

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#29

Re: Different Countersink Bits

04/21/2016 8:26 AM

I like your style out of box experience.

All the countersinks would work in soft material, my favourite for the job would be the last one, looks like bullet bill. If the material gets hot it will become hardened instantly and even a carbide would struggle. My own example was drilling a stainless sheet, went in with a 2mm pilot, heated up the area so it went blue, couldn't get a 5mm drill to touch it. However, straight through with a 5mm and no pilot, no problem. A technique for keeping the heat down in cnc'ing, is using the swarf, large swarf will take an amount of heat away. as you have noted, there are differing opinions, maybe only trials will answer your particular situation.

cnc jim

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#32
In reply to #29

Re: Different Countersink Bits

04/21/2016 9:02 AM

That is an excellent point to make cnc jim. If they really wish to get "technical", they should look into other more efficient ways to make the holes in the first place, such as laser cutting or water-jet cutting. No heat or impact hardening of the metal around the hole.

One of the hardest things to get right using stainless steel is cutting pipe threads on fittings, and the one harder than that is getting the threads to fully tighten to a seal (even on the tapered threads of a standard pipe thread taper), due to the tendency of the stainless steel to localize heat to such an extent that galling of the metal ruins the thread surfaces. One has to engage such threads incrementally, and very slowly, otherwise galling will take place, so much so, that it is better to use black polypropylene pipe fittings against stainless steel ones (no sealant required in that case), where the application temperature and pressure allows for it.

It would probably help with advising if out of box experience would include a photo or three of the work piece and the equipment set up.

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#47
In reply to #32

Re: Different Countersink Bits

04/21/2016 11:17 PM

Cutting pipe threads on stainless is relatively easy if the correct equipment, thread compound are used and it is understood what causes the apparent galling. When st. stl. threads are cut very small, almost microscopic, burrs are formed on the sides of the threads. When the threads are tightened, from the start of them engaging to completed being tightened, these burrs can do several things. They can break off and fill the gap between the threads, become so heated that they friction weld themselves to the complementary threads or simply become suspended in the thread compound "dope".

When choosing cutters for the die always use ones for cutting stainless steel threads. Do not use ordinary cutters such as used for "black iron" pipe. They are not hard enough.

The following is a listing of hand die holder cutters from RIGID

Catalog No.
Nominal Pipe Size - Threads Per Inch
1/8-271/4-183/8-181/2-143/4-141-11 1/21 1/4-1 1 1/21 1/2-11 1/22-11 1/2
(NPT) National Pipe Taper
Alloy RH378103781537820378253783037835378403784537850
High-Speed RH378553786037865378703787537880378853789037895
High-Speed LH-3805038055380603806538070380753808038085
H.S. For Stainless Steel RH379003790537910379153792037925379303793537940
H.S. For PVC RH--70685706907069570700707057071070715
HS Reversible RH*---4970749712497174972249727-

The st stl cutters are different from those most commonly used.

The sealant (dope) used has to take the microscopic heat, reduce friction and be compatible with the material within the piping system. At least a good grade Teflon tape should be used and applied in the proper manner for the pipe size. There are several excellent Teflon pastes available such as Loctite 30554, 565 or others. There are tables which show that St Stl pipe threads with good sealant/lubricant properties require less than 1/2 the force to tighten them and can be tightened further than with regular sealants.

If the small burrs are reduced in size and quantity by using the correct hard thread cutters and a good lubricating thread sealant/tape are used the problems will almost always disappear.

I have worked with st stl pipe both threaded, welded, flanged, and other types for many years (more than I want to admit to) and have never had any problems caused by galling once I found out the right way to do it. Proper tools and proper sealants!

Good Luck, Old Salt

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#49
In reply to #47

Re: Different Countersink Bits

04/22/2016 9:07 AM

Instructive as usual. Good sound advice from a pro. Thank you.

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#43

Re: Different Countersink Bits

04/21/2016 2:27 PM

This thread has gone the way 99% of threads here go.

In the tank.

Everybody's got a pet way of doing this and their way is the best way.

Just give these guys multi-flute reamers, set the depth stop and tell them to bear down firmly but don't stall the drill press.

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#44
In reply to #43

Re: Different Countersink Bits

04/21/2016 2:42 PM

Ah, same old optimistic lyn.... Always the sunshine of the thread

Yes, a dozen different ways, but nevertheless, a lot can be learned from everyone's differing opinion.

And I've already bought the tool. Working fine so far. Thank you everyone.

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#45
In reply to #44

Re: Different Countersink Bits

04/21/2016 4:40 PM

You just have to sort the wheat from the chaff. Sometimes the chaff sorts itself out.

it's always good to get feedback if something worked or didn't work, for contributors and subsequent searchers.

cnc

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