End Mill Adaptors

An alternative to the collet for holding end mills, is an end-mill adaptor. Like collets, these are available in various tool shank diameters. For the Grizzly mill and HF MT#3 mill the ones you want have #3 Morse taper and M12x1.

75 thread to match the drawbar, not the more common 3/8-16 thread. You can use ones with the 3/8-16 thread if you make your own drawbar from a length of threaded rod, however.

The adaptors shown above were purchased from Grizzly for about $18 each. Go to the Grizzly site and search for “end mill holder”. Several times when I have ordered them from Grizzly they have been on backorder but this problem may be resolved now, since I recently (03/02) received a 1/2" adaptor that had been on backorder for several months.

Another good source is LittleMachineShop.com. They have a good selection of individual adaptors as well as sets of five for different shank diameters. Here’s a photo from their site of one of the sets, which sells for about $80 (03/02).

LMS End mill set, 1162

These adaptors hold the milling tools very rigidly (some users argue that they are more secure than collets) and provide some extra clearance for the tool below the head.

This can make it easier to view the cutting operation in some cases where the cutting tool might otherwise be hidden by the head.

Here are some informative comments posted to the 7x10 group by Rick Kruger:

> Collets will work but if not snugged up tight enough, the end mill can move, downward usually, increasing the depth of your cut, which can cause significant problems (eg. ruined parts, crashed head, broken gears, etc). > > There has been a bit of discussion previously about not over-tightening MT3 collets due to the heavy hammering it takes to release them and potential damage to the spindle bearings.
>
> If you use the collets, I would tighten them very well to ensure the endmill doesn’t move. > > Then, when hammering (deadblow, not steel) on the end of the drawbar to release it, support the bottom of the spindle with a hunk of keystock, round, or wood block, wedged between the lower end of the SPINDLE and the table (not the end of the collet or the under-side of the mill head). This way, the blows to the drawbar will be transmitted to the table and not spindle bearings.
>
> End mill holders, due to the set screw, generally don’t have the problem of the end mills working loose. But then, carbide end mills don’t have a set screw flat, so they could work loose if the set screw isn’t tightened enough, and maybe even then (I worry about it).
>
> Both collets and end mill holders require drawbars. The drawbar that comes with the mill is metric, as are the collets. > > I found it hard to get matching metric end mill holders (always backordered), so I got 3/8"-16 holders and use threaded rod & a nut for a drawbar. Works just fine.
>
> I have two end mill holders and a 1/4" - 3/4" by 1/16" set of collets. I use the end mill holders for most of my milling and buy HS end mills with 3/8" and 1/2" shanks whenever possible. > > For 3/8" and 1/2" carbide end mills. For other sized HS and carbide end mills, I use the collets.
>
> As far as double ended end mills, it depends more on the length of the flutes. My collets can take up to 1-3/4", the 3/8" endmill holder up to 2-1/4"