A Very Simple Arbor For Horizontal Mills

One of the most common complaints regarding horizontal milling machines is acquiring a good arbor for the cutters. These machines are always old ones and the existing arbors are always bent, even if only .005 or so. I was fortunate in acquiring a beautiful relatively new (1954) German horizontal mill with 1 inch and 7/8 arbors that are straight as an arrow.

But it does take some time changing over tooling with a normal arbor so I devised something a little different. I bought a ER-40 collet chuck with a CAT 40 shank to fit my mill. I envisioned using one inch shafting or drill rod to make an arbor that could be secured in the ER-40 collet and supported at the free end with the normal over arm. There’s nothing particularly unique about this except that I eliminated the large nut that normally clamps the cutter(s) and various spacers.

I decided to use a thrust washer against the over arm bearing, and applying pressure using the over arm crank. This system elimates expensive CAT 40 arbors. The new arbor couldn’t be simpler: a length of 1 inch shafting or drill rod, cut to length and slotted for a key (to prevent the cutter from rotating during the cut) and one end turned to fit the over arm bearing..

It took a while before I actually made the arbor but I finally got around to making a short arbor from one inch drill rod to be driven from the previously mentioned CAT 40/ER-40 one inch collet chuck and secured with the end support. The original plan was to use opposing keyways to minimize distortion in the arbor but I decided to try one very short one first. I have less than thirty minutes total into this and it can't get much simpler



Here's a slotter on the arbor, set up for a test cut.



As described earlier, there is no retaining nut, the assembly is held in position by the end-support with slight preload against a thrust bearing (no helical cutters = no appreciable side loading). Here's the test cut.



The idea is to end up with a half-dozen short arbors permanently loaded with common slotters (and a couple of slitting saws) for light work. … so far, so good … takes about one minute to change cutters. Before making any more arbors, I'll use this one for a while, checking runout occasionally to see if the arbor distorts with age and use.

A cautionary note: the ER-40 collet requires a LOT of clamping pressure to transmit the torque required by larger cutters. I welded a one foot length of 1/8 black pipe to the handle of the spanner wrench normally used to tighten the collet holder. Placing the mill in back gear and applying some grunt, the cutters can be held securely.

Even so, for safety sake, I usually traverse the table manually, rather than using the power feed, so that I can feel if something is amiss. Of course with the conventional CAT 40 arbors, power feed is not a problem.

Here is a photo depicting a normal CAT 40 arbor at the bottom of the picture, with a couple of spacers loaded on it. In the upper part of the photo, the new short arbor is shown. I made it short for stiffness but there's no reason why it can't be as long as a standard arbor.



Loading and unloading tooling on this arbor takes less than 1/4 the time required for a conventional arbor.

Sorry, I must be missing something? Besides the key, is the cutter just floating on the shaft?...Dave

chips&more said:

Sorry, I must be missing something? Besides the key, is the cutter just floating on the shaft?...Dave

Click to expand...

No, the cutter has standard one inch spacers on either side of it - they were removed for the photo and can be seen above the arbor. The thrust of the over arm bearing applies sufficient pressure, through the spacers to the cutter, that it doesn't move laterally. The key, of course, prevents the cutter from rotating.

The mill is set up with a standard arbor at the moment. After finishing the existing work, I'll remove the standard arbor, install the short arbor and make a good photo so that the entire setup can be seen.

Thanks for bringing this up, I should have mentioned it in the original post !

PS: In the second photo above, the two spacers can be seen, mounted on the arbor and securing the cutter.

OK, thanks for getting back to me. My overarm does not have any thrust bearing. It has an adjustable spilt bushing and just holds the outboard end of a shaft firmly in place…Good Luck, Dave.

chips&more said:

OK, thanks for getting back to me. My overarm does not have any thrust bearing. It has an adjustable spilt bushing and just holds the outboard end of a shaft firmly in place…Good Luck, Dave.

Click to expand...

Dave, if you haven't already considered this, it's easy enough to add a thrust bearing inboard of the split bushing (mine is also a split bushing design), either bronze or ball/needle type, slipped over the arbor. The ball/needle option seemed like overkill to me since my machine rarely exceeds 200 RPM

There's really not much pressure required to hold the cutter in place IF it's not a helical cutter. In fact, I would never use a helical cutter on this simple arbor without modifying it for a lock nut. That would sort of defeat the quick change intended purpose however.

Again, thanks for bringing up this topic since I omitted the details originally !

Awesome thread! Thanks Randy!

Nice job, do you have a face cutting arbor? I liked using one in my apprenticeship training shop. We had at least one bent arbor. Don't know how or who bent it before I got there. They had a shop full of old machines to train on. Once outside that shop there new modern grinders and milling with DRO's in the repair shops.