I'm relatively new to this so please accept my apologies if I make some errors.
I have previously had some experience, under limited supervision from a trained engineer, on the Bridgeport. I've now purchased one for my own use which has been supplied with some tooling.
All of the (rather ragged) end mills are screw shank and there is a chuck with various diameter tapped holders (collets?). Also supplied was a box of R8 collets (2mm - 20mm from memory).
I've previously used the screw-shank variants so I'm comfortable with them however I have no experience with the collets.
A few questions if I may:
a) Which method is better?
b) Dependant on a suitable diameter collet, do all "Plain shank" end mills fit in the R8 collets?
c) When I purchase new end-mills, which of the above would you recommend?
Sounds like you have a Clarkson autolock holder, are you familiar with their use?.
a) The Clarkson holder for the screwed shank cutters is better than collets as the cutter can't pull out under heavy cuts like it can with a collet.
b) As far as I know all cutters, be they screwed shank, Weldon (set screw retention), or plain shank are OK in collets. I have threaded shank and a few Weldon types and regularly use them in collets when the guaranteed retention given by the Clarkson holder is not required. Just make sure the cutter is inserted so the collet is holding the plain section.
c) Depends what you're doing. If you're not taking heavy cuts then the threaded shanks for the Clarkson are not required but I buy most of mine as threaded shank in the larger sizes. 16mm being the largest I normally use. Not noticed much difference in the price, I often buy tools when on sale from J&L UK.
Many thanks for your detailed reply. I have noted your comments.
I've used the screw shank cutters and holder before but I didn't know the correct name for them - thanks. Looking on the web, the autolock inserts appear to be threaded but the ones supplied with my machine aren't. They just slip into the holder and are held in place by the retaining collar, tightened by a spanner. Is this still a "Clarkson autolock"?
The engineer who was showing me the ropes recommended that the screwed end of the cutter protrude slightly (maybe 1mm+) from the end of the holder before it was inserted into the sleeve and tightened. Is this correct?
I haven't managed to break anything yet and I'm keen to keep it that way!
I jumped to the conclusion you had a Clarkson autolock holder when you said threaded shank cutters but was wrong by the sound of it. Have a look here for some different collet types.
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. At a guess I might think you have an ER collet holder as they don't have threads in them and are quite common, see
O.K. There are four ways that I know of to hold end mills in a Bridgeport, and one of them is quite uncommon in the USA, though quite common in the UK. I'll describe that one first:
1) Clarkson end mill holders:
The last few mm of the mill's shank is threaded, and threads into collets which fit into the holder. The holder has a projecting center which bears on the center hole of the end mill.
I've got a couple of sizes of the holders, and none of the end mills for the NTMB 40 spindle of my Nichols horizontal mill.
This style of holder has the advantage that the end mill cannot shift its projection during cutting loads (unlike the R8 collets.
There are collets available for this to fit metric size shanks, and fractional inch size shanks. The ones which I have are all fractional inch sizes. I wish that I could buy the collets at reasonable prices here in the USA -- just so I can try it at least. :-)
2) Shrink-fit end mill holders:
Also uncommon -- except in serious production shops in the USA (and perhaps elsewhere). The hole in the end mill holder is just a little smaller than the diameter of the shank, so the holder is heated and the end mill is inserted before the holder can shrink again. I've never used one of these, but I have the feeling that once an end mill is inserted, it is there for life.
And I don't know whether these have setscrews in addition to the shrink fit or not.
3) Setscrew end mill holders:
The best bet in the USA where the Clarkson holders and end mills are not readily available. The end mill is inserted, and the flat-bottomed setscrew with a bevel edge is tightened. The bevel on the end of the setscrew encounters a matching bevel at the top end of the Weldon falt onto which the screw tightens. This keeps the spiral of the end mill from pulling it down and thus starting to cut deeper than you planned.
4) R8 collets:
The most common US way of holding end mills -- but the spiral of the flutes can cause the end mill to walk down in the grip of the collet during heavy cuts, resulting in damage to the workpiece, and occasionally damage to the table or the vise as well.
Note that R8 collets have a very small range of contraction, so you can't mix metric collets and inch shanks or vice versa.
To my mind, the Clarkson system -- if that is one of what you have. Your description was a little unclear to me.
Second would be the setscrew type of end mill holders, if you can get end mills with Weldon flats.
Third (for convenience) would be the R8 collets -- but be careful when taking heavy cuts.
Forth would be the shrink fit holders -- if only because a hobby user can't usually afford to expend an end mill holder when an end mill is no longer useful.
Metric size end mill shanks fit the metric R8 collets (which it appears you have). Fractional inch end mill shanks fit fractional inch R8 collets. *Don't* try to stretch a collet to hold a larger size, it will only lead to disaster.
If you have the Clarkson holders, go that way. I don't know the relative cost between Clarkson end mills, ones with Weldon flats, and ones with purely cylindrical shanks, but if the cost of the Clarksons is not prohibitive, it is more likely to prevent damage to a workpiece which already has many hours of work invested in it.
While you are at it -- you also want 2-flute end mills for cutting slots, and ones with more flutes (four and six are common in my collection) for milling from the side.
There are also "roughing" end mills for fast material removal, and the standard ones for everything else.
For the record, these are pretty pricey for hobby work, and their real payoff is in handling tools for use in high-speed mills -- 10,000 rpm and up.
Also for the record, the heaters, which use induction heating, will seat or release carbide-shank tools without trouble. But only the best ones (mostly made by Bilz, often re-branded by other tooling makers) will reliably
*release* a HSS-shank tool. The coefficient of thermal expansion is about the same for tool and holder, and it requires a really quick heating to expand the holder without swelling the tool shank too much to release.
I think the prices will make most hobbyists' eyes roll back in their heads. But they're really slick and they work great.
Perhaps. It depends on how much better they are at keeping the cutters from creeping down under heavy cuts. If they are the same, just lump them with "R8"s with a higher cost added on. :-)
There are also the quick-change tool systems, including the one for the Series-I CNC version of the Bridgeport which uses NTMB holders, which can be endmill holders or collet type.
There is another quick-change system which fits into the standard R8 spindle.
But both of those are more likely to be found on CNC versions of the Bridgeports, not on manual ones.
ER is not the only type of collet chuck, there's the Universal type which looks similar but has fewer slots and doesn't have the groove where the two angles meet (a Universal ZZ set came with my Index mill). I believe there are other collet systems as well. --Glenn Lyford
That certainly is -- or a clone if such are made. You will probably find "CLARKSON" engraved in the edge of the nose-piece.
I think that is a J-1 tyle -- the side covers say that it has step pulleys. Look at the text stamped in the left-hand of the two nameplates side by side. If it starts with a 'J', then you do have a J-head. The '1' would be a 1 HP motor. Or maybe the serial number is under the gray paint lower on the head.
Mine is a J-2 head made for a CNC machine (BOSS-3) so the feed hardware is replaced with a ball screw surrounding the quill, and the motor is hung from the underside of the casting instead of the upper side, as well as mine having a variable speed crank in place of your step pulleys.
If it has an R8 spindle, I don't think that it can be an M-head. I think that they used Morse taper collets instead.
Thanks for providing a picture of your disassembled Clarkson Autolock collet parts, Mike. I haven't seen them before, and I wouldn't have known what they were, if I did see them.
What is not shown by the photos is that there is a thread on the shank end of the end mill (just the last 3/16" or so) and a matching thread on the bottom of the collet.
The center hole in the shank end of the edn mill engages the center pin in the bottom of the holder's pocket, and when the nosepiece is screwed in the taper inside the nose piece closes the outer end of the collet to firmly center the end mill.
There is no way that a right-hand end mill can come out of the holder with cutting forces. (Hmm ... I wonder whether there are left-hand cutting end mills for the Clarkson system, and if so, whether they have correspondingly threaded collets?) Anyone out there ever seen left-hand end mills and collets for the Clarkson system?
BTW When I first started searching on eBay for Clarkson holders and end mills I was driven nuts by constant hits on "American Idol" DVDs. I had no idea why, never having wasted my time watching that show, until I saw that they were featuring a "Kelly Clarkson" as a singer. :-)
Thanks for the additional details, DoN. As I looked at the parts I wondered if this tooling could be used to drive a tap for tapping, or if the threaded parts would just separate if the spindle was reversed.
But then, I don't know if it's even practical to tap threads with a Bridgeport mill.
How would you deal with the needed feed per revolution? This is mostly a CNC type job with a rigid tap holder. (After all, it takes a lot of force to pull the spindle down with the tap threads, so it is more likely to break the tap or strip out the starting threads.
With a manual machine -- yes with the proper accessories.
Look at the various tapping heads (excluding the rigid ones). A good example (and what I use in two sizes to tap even on a drill press) are the ones made by TapMatic. It is a cylinder mounted between however you drive it (I use a MT-2 shank in my drill press, or would use a collet or a specially machined R8 or NTMB 30 or 40 shank on my mills) and the special tap collet chuck which has Jacobs Rubberflex collet (typically two sizes to cover the range for a given tap chuck) to hold the tap concentric, and a pair of steel plates which clamp down on two flats of the square at the back of the tap for driving it.
There is an arm protruding radially from the bottom of the cylinder, which needs to contact some part of the machine to prevent the whole outside of the cylinder from rotating.
The collet spindle has quite a bit of end play, and three effective positions.
1) When the tap chuck is fully withdrawn, the chuck rotates at the same speed as the drill press or milling machine spindle, and allows a certain amount of motion to allow the tap to self-feed a certain amount. Normally, you feed by hand at about the speed that the tap feeds into the workpiece. (Use a gun tap, of course, not a hand tap which needs frequent reversal.)
2) In the middle of the range, it disengages a dog clutch in the housing, and allows the tap to stop while the spindle continues to rotate. Normally, you set the depth stop on the machine to stop it before you reach the end of the threads on the tap, or before you reach the bottom of the hole on a blind hole.
3) When you start to withdraw the spindle, you engage a set of planetary gears in the housing which starts the tap rotating backwards at a somewhat higher speed than the spindle's forwards direction.
With your other hand, you squirt a good tapping fluid on the tap just before it enters the hole.
As I said above, I have two sizes of these TapMatic heads.
A) The smaller one goes from an 0-80 to a #10 or #12 -- and can handle 1/4" in some materials. This one has an adjustable torque limit clutch. You adjust it so it just barely does not slip with a *new* tap and in the workpiece material which you are using. When it starts to slip, it is time to replace the tap, because it is getting too dull to trust in your workpiece.
B) The larger one will go up to 1/2" taps, and instead of the torque limit, it has an adjustment of the free feed before the dog clutch disengages. This is better when you are tapping near the bottom of blind holes. Otherwise, you leave it with lots of travel (1/8" or more, IIRC) when tapping through holes.
I believe that you can get both styles in both sizes, but when getting things from eBay auctions and swap meets, you take what you can get.
Some of them have a Jacobs taper in the back to accept your choice of Morse taper arbor or whatever fits your machine.
Both of mine have a threaded hole instead, and I had to thread No. 2 Morse Taper blanks to fit -- each has a different size of threaded hole -- and the first one I got (the smaller one) had an adaptor with it to fit a Turret drill press -- which is probably why I got it for such a good price from eBay. :-)
There are other brands which are well thought of, but I can't remember the names at the moment, since I don't have any examples. :-)
Be aware that the method of tightening a Clarkson collet is not in my mind intuitive! The correct way to fit a cutter is as follows Screw the cutter into the collet a few turns. Insert the cutter and collet into the nose piece. Screw the nose piece into the chuck body until the mating flat faces touch. If the position of the cutter stops this then unscrew the cutter until the nose piece can be screwed up to touch. Screw the cutter up until it is solid. Tighten the nose piece with a spanner.
The only tapping under power that I've done has been on lathes, DoN. I thought it might not be practical to tap on a Bridgeport with the tap secured by a collet.
Most of the time, I tap by hand with a tap handle, or using a drill press like a tapping fixture hith a hand crank (without using the motor) with the taps held in the chuck. No, not the slippy method, I've ground 3 flats on the shanks of a handfull of taps for holding them in chucks. A hub for the hand crank is permanently installed at the top of the DP spindle and the crank fits in place by sticking the 2 protruding pins in the crank handle into 2 holes in the hub (no screws or other fasteners involved). I can loosen the belt, disengage the quill return spring, and attach the crank in about a minute.
If one were to use one of those shop-made telescoping tap holders for a lathe tailstock, I suppose that the tap self-feeding itself wouldn't be an issue whether it was used on a mill or drill press.. correct?
I've seen tapping heads like the TapMatic in catalogs and more recently in videos, and have read numerous RCM posts about how slick they are. I've read a lot here in RCM, and when contributors like yourself, and at least several others, take the time to write detailed commentaries about metalworking topics, I always take the time to read them.
As I've stated before, anyone that spends any significant time "on RCM" would be doing themselves a great disservice if they aren't reading all the really good comments concerning all the widely varied metalworking topics.
Some folks like to read a morning paper.. I read RCM instead, nearly every day, maybe missing a couple per month.
Fortunately, most of the contributors of the metal related content are talented at describing their thoughts well in text. Perhaps most fortunately, those frequent contributors have been willing to stick around to continue sharing their experience(s) and helping others, despite all the non-metal noise that takes place regularly.
The anniversary of the loss of one of the great RCM contributors will be remembered/observed soon.. RIP Tnut
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