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Countersinking - guidance please...?

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RJKflyer06/06/2010 17:56:44
49 forum posts
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Just been countersinking some mild steel and been rather surprised by the exceeding poor cutting ability of the countersinks I have - set of 3-flute HSS from RS. I'm countersinking a 7mm hole to about 12mm overall (for an M6 CSK).
 
It was all very nasty with considerable chatter. Given that in my Wabeco mill i can use a 2.5 inch facemill without it dropping speed at all, runout is imperceptible,  and i can drill/mill up to at least 12mm (so far) with fabulous accuracy and surface finish, I'm going to blame the countersinks. It was all rock solid in a decent mill vice too.

I also tried a Nine9 indexable 90 degree spot drill (brilliant for chamfering!), but to be fair i was at too great a diameter (over 75% of the diameter of the insert) and this didn't like it a lot either.
 
In the end, I  used the 21mm countersink at high speed (2500 rpm) and just faced off a fraction at a time to get a decent finish out of the rough countersink I had already got. It's good enough now but not an experience to repeat.

I did notice that on the 3-flute 21mm csk, one of the flutes actually showed a slight scuffing on the ground section a couple of mm behind the cutting edge - in other words looks like that particular flute isn't even ground such that the edge is actually cutting!
 
Now folks, can anyone advise me around a solution to this? Am i missing anything? Or is it just that i need to go buy a really decent countersink? In which case - suggestions? (Guess the RS stuff these days is Chinese...)
 
 Thanks!
JasonB06/06/2010 18:42:40
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25215 forum posts
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You are running way too fast, put it on the slowest speed and use a little cutting fluid
 
As for makes then Hall or Ruko are both good, Try J&L or even Screwfix do some of teh Ruko ones
 
Jason

Edited By JasonB on 06/06/2010 18:45:58

Steve Garnett06/06/2010 19:01:15
837 forum posts
27 photos
Agree entirely with Jason - 2500rpm is a ridiculous speed to run a countersink at! I would have thought that 250rpm was as much as you'd ever need, and even that's a bit fast for some bits.
RJKflyer06/06/2010 19:06:21
49 forum posts
3 photos
Please READ my post - the 2500 was just to face a FRACTION (i.e. few thou) off the rubbish initial cut. It's mirror smooth.
 
I ran the original cuts at 300 rpm but had terrible results. 
RJKflyer06/06/2010 19:14:16
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And my 300 was based on ca. 2/3 the speed you'd drill at 14mm, or thereabouts.
JasonB06/06/2010 19:19:45
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300 is still faster than I would run a CSK bit at that dia in steel I'd be looking at 50-100rpm
 
Jason
John Stevenson06/06/2010 21:40:13
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Get the TiN coated single flute made by M A Ford in the USA, J&L sell them.
 
I once spent over £200 buying one of many different types for a large job so i could test them out. The M A Ford ones out performed all the others, even solid carbide ones.
 
I have a twin spindle drill and one spindle is driven by a geared motor at one speed, it can't be changed.
This spindle does 70 rpm and is used solely for countersinking and counterboring.
some of my jobs require countersinks of 30mm diameter and these cutters do this with no problems.
 
John S.
Steve Garnett06/06/2010 22:04:24
837 forum posts
27 photos
Posted by RJKflyer on 06/06/2010 19:06:21:
Please READ my post

Did read it - the only speed you mentioned at all was 2500, so we had no idea what speed you'd used originally. So I suspect that both Jason and I assumed that it bore some resemblance to the 2500, I'm afraid - sorry about that. In terms of stress and strain on both the tool and the work, countersinking is up there with the worst - it really does work best done very slowly.

Ramon Wilson06/06/2010 23:45:56
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RJK, I have to agree with all the guys above, countersinking is one operation that defies the normal laws of cutting speeds of materials and needs to be carried out much slower than you are doing - most times as slow as possible to achieve a reasonable finish.
 
Countersinks come in many guises but all will chatter to a greater or lesser extent if run too fast. This normally produces a ribbed surface radiating outwards all round the counter sink. By reducing speed to the slowest possible, if you have a controlled fine feed, this can usually be removed by using very slow down feed. If however it is hand fed ie on the drill machine this becomes far more difficult as the C'sink 'rides' the ribbing. This can however, with care, be over come by tearing a piece of emery cloth into a small square  big enough to cover the hole then with the emery surface uppermost  and again at slowest speed bring the C'sink down firmly into contact with sufficient pressure to allow it to cut through the emery. The emery somehow takes care of the ribbing effect and allows the C'sink to cut evenly. This tip was shown to me many years ago and has been used many times both at home and at work to 'reclaim' a poorly formed counter sink.
 
Regarding speed for this op my Fobco drill press has a low speed of 400 or so rpm which is far to fast for all but the smallest of holes. To overcome this lack of slow speed for this operation a second motor is bolted to the wall and this drives the drills motor pulley at a reduction which in turn is set at its slowest speed. I can now get about 40 and 80 rpm which is perfect for C'sinking  and tapping.
 
Hope this helps - Ramon

Edited By Ramon Wilson on 06/06/2010 23:47:55

chris stephens06/06/2010 23:59:28
1049 forum posts
1 photos
Second John S, re single flute countersinks. I bought one about 20 years ago, it was reasonably expensive at the time but worth every penny. What's that about 'the quality is remembered long after the price is forgot'? Unfortunately there is no name on the tool, so i can't  recommend a band.
Just looked in J&L catalogue, and mine  looks much like the "select" single flute, but without TiN coating. I don't think TiN coating was commonly available back then and the price is about the same, but 20 years apart!
As for use, a slow speed, a positive down feed and set the depth stop, this last bit is fairly important.
chriStephens 
Ian S C07/06/2010 02:52:06
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Not sure what the name of the tool is but I have one of those countersinks with a conical end with a hole through it, this is excelent, as with all countersinks it needs to run slowly.Ian S C
RJKflyer07/06/2010 09:07:59
49 forum posts
3 photos
Thanks guys. Looks like a decent SINGLE flute is the preferred route?
 
I've tried others from this set i have, and three of them work 'fine' - or at least as fine as i will get from them i suspect. No terrible chatter and reasonable finish etc.
 
With the duff one, no amount of slow speed and lube will make me want to use it - it's just too vicious. 
 
Thought you'd be interested in this one that led to the thread: photo attached. If you look at the 'land' i have photographed, you'll see it's buffed hard well back from the cutting edge. I've only used this one once.
 
Worth me sending back do you think?

 
RJKflyer07/06/2010 09:08:31
49 forum posts
3 photos
Oh, and Ian SC - it's a 'deburring' tool i believe...
Ramon Wilson07/06/2010 09:24:09
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1655 forum posts
617 photos
Hi RJK
This looks like a definite candidate for replacement if they will.
As you have photographed it there appears to be sufficient backing off but obviously there is some kind of land that is rubbing and 'picking up'. If they wont change it perhaps a stone rubbed across that point to reduce the area might improve matters.
 
FYI I have several types of CS - single, three, and multiflute as well as the type that Ian SC mentions - No real preference they all do a reasonable job but the hole type does cut very well though the cutting area is somewhat limited  compared to other types subsquently the need for several to cover various diams.
 
Regards - Ramon
KWIL07/06/2010 09:25:27
3681 forum posts
70 photos
I agree the single hole tools work well for deburring but for countersinking I always use a 3 flute TITEX brand (German) TIN coated. The finish on the TITEX tool however is almost mirror like, unlike the roughly ground example in the RJKflyer photo above. Speed is usually on the back gear on the mill so that is  under 100 rpm and keep the pressure on, right on to where the depth stop is set.
Eric Cox07/06/2010 09:37:29
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557 forum posts
38 photos
The idea of the counter sink is to bring the screw head flush with the parent metal. Does it matter what the finish is like?.
Ian S C07/06/2010 10:55:23
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7468 forum posts
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RJKflyer, yep thats the one,it makes a good counter sink also. I go along with The emery cloth for ordenary cutters, or a drill bit sharpened as a counter sink. I'v got two or three that I'v made from old center drills that work fine. If you make your own, try not to get the flutes evenly spaced, it will then cut chatter free. Ian S C
Geoff Theasby07/06/2010 14:32:36
615 forum posts
21 photos
I have had lots of trouble with countersinks chattering.   After trying the single diagonal hole type, I have used no other.   Even cheap ones work well.
What does it matter what the finish of the hole is like?   If it chatters, you get a multi-faceted hole rim which shows all around the screw head, that's what.
Gordon W07/06/2010 14:50:50
2011 forum posts
I used to have c/sinking trouble on little bench drill, until I realised you must go slow, revs and feed. Just look at the width of cut. I 've 3 c/sinks,one a multi groove thing ,useless except on wood, two 3 face ones, one made in Germany,tother no name, both work very well
Mike07/06/2010 15:25:54
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713 forum posts
6 photos
Like Geoff, I have used the single diagonal hole type for more than 20 years, and no chattering whatsoever, even on relatively hard stainless. Just use them at very low speed. I think they are correctly termed de-burring cutters. Can't find a source on the internet at the moment. Does anyone know of one?
Mike
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