How can collet grip be improved?

[dave49]

I am having trouble with small end mills migrating up or down in a WW collet. Full details at Collet Grip | North Branch Reels
Any suggestions?
Dave

 

[abarnsley]

Use a better collet system.. ER8 etc...

Or make endmill holders... Or run straight flute end mills..

Hard tool shanks, have never gripped well in R8 type (WW is close enough) collets. That is why there are endmill holders, and much more flexible/better gripping collet designs..

 

[CalG]

I am having trouble with small end mills migrating up or down in a WW collet. Full details at Collet Grip | North Branch Reels
Any suggestions?
Dave

Read up some time regarding the recommended torque spec for the ER collet system. You will be impressed, the numbers are large.
Applied to just about any other collet system, most tools would be quite secure.

It says something about the effort at the number of R8 pull rods that have the threaded portion pulled off.

 

[lionelt]

I am having trouble with small end mills migrating up or down in a WW collet. Full details at Collet Grip | North Branch Reels
Any suggestions?
Dave

Could you drill through the side of the collet to take a dog point set screw, and grind a small flat that lines up with this on the end mill?

 

[Big B]

Make sure that you have a film of oil on the taper and in the threads and that the hole for the cutter is dry and clean. That is where I would start.

 

[Milland]

This thread: http://www.practicalmachinist.com/vb/general/8-millimeter-lathe-chucks-w-w-167749/ indicates that WW collets have a 40 degree cone angle. This is rather steep, and means that you're not getting as good compression on the tool for a given amount of drawbar tightening.

If you don't mind the risk, and are willing to replace collets every so often, you can buy some fine diamond grit (as meant for lapping), and apply a light coat to the OD of the tool and then tighten into the collet. Don't let any of the grit get onto the collet OD! The diamond will bite into the tool shank and collet bore, helping to lock it in place. Something like this might work: 1 Bottle THK 2 5 Micron Diamond Polishing Lapping Paste Pastes Compound 2 Gram | eBay

 

[L Vanice]

I am having trouble with small end mills migrating up or down in a WW collet. Full details at Collet Grip | North Branch Reels
Any suggestions?
Dave

The WW (Webster-Whitcomb) is the common American 8 mm watch lathe collet. Millions have been made and most will do what they were designed to do which is basically lathe work. Eventually, the lathe makers built milling attachments for the watch lathes, but that was before the modern end mills were available. Most of the watch lathe collets are metric with .1 mm increments available, but Derbyshire, Levin, Starrett, Schaublin and possibly others made them in fractional inch sizes by 64ths. Some are better than others. The largest through capacity of the WW collet is either 5 mm or 3/16 inch.

I would suspect the slipping end mill is caused by a substandard collet, asking too much of the machine in terms of metal removal rate or a substandard endmill. The "full details" left me with questions. I do not know who made your spindle assembly, so there is a chance that the spindle dimensions do not correctly mate with the collet. I do not know who made your collet, so it may not be of standard dimensions and accuracy or properly hardened. I do not know what sort of end mill you are using, so it may not be of optimum geometry for the material you are cutting.

The first thing I would do is get a good 3/16 inch or 4.8 mm WW collet and 3/16 shank end mills. There are many variations of 3/16 shank end mills available: cutting diameter, length of cut, number of flutes, helix angle, HS or carbide etc. The larger diameter shank will give a much better grip than the 1/8 you complained about. End mills with 1/8 shank are less popular. You can find a nice selection of solid carbide single edge engraving cutters in that size, ideal for engraving brass.

Manual machine tools are fed with cranks, so the operator has constant feedback concerning the cutting forces. A CNC mill will just try to do what the computer tells it, right up to the point of destroying itself. You have to be cautious with selecting the parameters you plug into the program.

There was a high quality WW spindle made for the Unimat SL lathes that is suitable for use in a milling machine. They turn up on eBay occasionally, but usually bring a few hundred bucks. Might be reasonable compared to what else, if anything, is available these days. The Levin WW milling/grinding spindle, for instance sells new for $1600. They ask $160 for a new 3/16 WW collet. Used stuff is usually a better deal.

Larry

 

[dgfoster]

From your website I see you already tried an end I'll holder without success:

"I have a lot of 3/8 end mills, so I also bought a 3/8 inch “end mill holder”. It has a set screw and so is suitable for HSS and cobalt steel end mills that have a flat. It does not help to hold a carbide end mill that has no flat."

If you have not already done so, you might try grinding a "flat" (divot might be more accurate) on the end mill shaft. I'd be surprised if that did not work. It need not be very precisely done. The simplest method to make the flat would be to use a "green wheel" on a bench grinder being aware of the health hazards of green wheel dust.

Denis

 

[grinderguy2]

Hi Tim here, I re-grind end mills all day. an easy way I have found to greatly enhance collet grip is to take a single wrap of paper .004" thick once around the shank. I have a small plastic divided box with a cardboard master and many paper wraps pre-cut for each size shank that I encounter. You can make the papers as tall as need be to suit you. do not overlap as it will (like the set screw ideas) "push" the end mill slightly off center.Tighten down as usual. This gives you that much more grip force without distorting. It is easy release if the tool gets warm with use, and can be reused often many many times(as I put many thru the same operations). Cheap and easy.
Have a great day

 

[TDegenhart]

Hi Tim here, I re-grind end mills all day. an easy way I have found to greatly enhance collet grip is to take a single wrap of paper .004" thick once around the shank. I have a small plastic divided box with a cardboard master and many paper wraps pre-cut for each size shank that I encounter. You can make the papers as tall as need be to suit you. do not overlap as it will (like the set screw ideas) "push" the end mill slightly off center.Tighten down as usual. This gives you that much more grip force without distorting. It is easy release if the tool gets warm with use, and can be reused often many many times(as I put many thru the same operations). Cheap and easy.
Have a great day

A good collet would not allow for added thickness of .004" paper. A good collet will match the shaft diameter of what's put in it when tightened.

Tom

 

[Winterfalke]

Even using ER-25 one ER-32 collets I have found that endmills like to pull out under heavy load, and they have many times more holding force than you are dealing with. If you are taking cuts that heavy, I would suggest that you need to make the endmill holder work. It is very common to grind a flat (or gouge) for the set screw to grab on to, or you can just buy endmills with a flat already on them. They are usually marketed as having a 'weldon flat'.

 

[Red James]

From looking at the link posted I notice an excessive length of end mill shank outside of the collet. Try to minimize this length, even by using stub length end mills. That leverage will make end mills chatter, and that will make them move.

 

[Monarchist]

I am having trouble with small end mills migrating up or down in a WW collet. Full details at Collet Grip | North Branch Reels
Any suggestions?
Dave

High-speed spindle? Chatter? Use the same size a LOT?

Have a look at a shrink-fit endmill holder.

Different sizes needed and frequent swaps needed?

Then perhaps the "TG" collet system.

Bill

(Disclosure: 5C, Jacobs 9XX, ER-20, ER-40, and side-lock holders under-roof, long-since.
Adding TG 'soon', even so.)

 

[RC99]

If you bead blast the inside would that help grip?

 

[Frank Ford]

Last week I made a dozen collets from 1144 steel for my Deckel pantograph - they're tapered with 20 degree included angle, and when I started to turn a feature on the ends they just squirted right out of the 5C emergency collet I'd bored to match. Not wanting to give up on the project, I resorted to using a bit of thin viscosity superglue in the collet to hold my parts. That absolutely solved my problem, and I finished up the project without a hitch. I cleaned the inside of my 5C collet with acetone, added a bit of cyanoacrylate, locked up the collet closer, drilled, bored, reamed, faced and turned a groove on the end. After each one was done, I took the collet out, tapped the part out from the backside, cleaned up and did the next one.

I'm wondering about trying the same trick to hold carbide end mills that want to crawl up and down in mill collets.

 

[Milland]

Bill

(Disclosure: 5C, Jacobs 9XX, ER-20, ER-40, and side-lock holders under-roof, long-since.
Adding TG 'soon', even so.)

Bill, the TG system doesn't get a lot of love around here. I think it's regarded as "older tech", and there's newer shallow angle systems that work better (Pioneer SX, for example).

Edit: Corrected collet system supplier name

 

[michiganbuck]

Dave,

With using your end mill holder. Then pick up a simple surface grinder, mount a diamond wheel the width that will interfere with your set screw sides to the ground flat. Yes best done with coolant so a messey job for your shop Use a double set screw one on top of the other for the lock set with not pushing too hard but just snug then lock with the second set screw. The local cutter grind shop can do this simple job for you if not wishing to purchase a surface grinder. *Don't know if I have a suitable diamond wheel but will check..

A whistle stop flat is common with having an angle (5*)to the flat so the held device goes one way to snug to the shoulder of the flat.

**Just the double set screw might work with not having the flat on the end mill. ** A loose brass plug set in your end mill holder above the tool and with the two set screws should work well. If the tool can not move up into the holder it will hold much better.. ** grinding a point radius perhaps 1/16 to the set screw set on the tool will help.

XX Someone may say put some grinding grit in your end mill holder XXX that is a bad idea and will soon wear out your holder.

*Nice reels and great web site.... We will be going to the Detroit Rive Wednesday for wallies.

My kellyroadcamp is only 60 miles north off 33 at Mann Road(east). I may have some good fish in my back pond as I think it has never been fished..at least not in the last 39 years. Yes it ices over but has springs leading in all winter.

Lovells Township in Crawford County, Michigan - Since January 8, 1912

OT: what is that beg bear area up Kenney road?

Buck

 

[dgfoster]

One comment on the Weldon Flat. It is a time-honored and nice looking feature found on a large variety of round tooling. But, for this particular situation, a "crudely" ground divot may be better. By divot I mean a just making a depression in the shaft say .030 deep and of a contour similar to what would be made if you could just intersect the shaft of the EM with a similar-sized EM. I'd use a simple green wheel to do that.

The advantage to the divot over a flat is, as alluded to by Buck, the flat has no lowest point. So, this slippery EM can migrate up or down a bit as limited by the flat dimensions much as the smooth-shaft EM can migrate without limit. Not saying the flat would not work. It's just that the cruder solution may actually be better in this case and requires only the purchase of a green stone for your bench grinder. (Use a good canister-type or equally effective air face filter to avoid the green stone dust.)

Denis

 

[michiganbuck]

QT Denis...
divot over a flat or hand green wheel flat.. Have done that often.

I know I have a green wheel always mounted.. You could mark them where you would like a simple flat and I could run them for the price of postage if you wish.. will send my phone number and address this afternoon.
Buck

PM sent

 

[jim rozen]

Please detail the drawbar assembly for this engraver spindle.

If it does not have a thrust bearing at the top, you will never be able to
develop full holding power. Plain drawbars basically suck at applying
draw-in force to the collet.

Thrust bearings can be loose balls in a cage or flat roller assemblies. You
can probably purchase an off-the-shelf flat roller assembly close to WW spindle
size.

Here's a home-made version for 3C collets: