Some observations on shared mill cutters

ericc

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A couple of months ago, I joined the Techshop. I needed to make some tooling for my lathe, and figured that the use of their large mill was worth the membership for a few months. The instructor in the mandatory basic use course advised the class members to provide their own end mills since the ones available at the facility were not that great. They were those boxed Harbor Freight type sets. The WWW has a lot to say about these sets, but here are some of my observations. The first project was to cut some 3/8" slots for a small lathe faceplate. There was only one end mill cutter less than 1/2". It was 5/16", and it looked dull and burned. It seemed to cut OK, and I was able to finish the project. It did strain a little at 0.1" DOC, but was fine at 0.05", although it tended to throw off heat colored chips.

The next day I came in was a few weeks later. It was really hard to get the time to do this, and that was also a learning experience for me. The project of the day was to trim the bottom of my new boring bar holder and make a vise tilt table. For this, a 5/8" end mill rolling around in the tool cart was selected. The only marking on it was a big "CHINA". It worked great. Quiet, no colored chips, cut well and smoothly. It was able to get the job done quickly. The faceplate was done, but there was a little spot I missed, so I searched for the lonely 5/16" bit in the tool drawer. It was there, but it was in even worse shape. There was aluminum welded to the flutes that was stuck so hard it could not be removed with long nosed pliers. I had read that cutting steel with a lot of soluble coolant would remove the aluminum, and since the touch-up would use the side flutes, it was tried successfully.

So, the bottom line is that the selection of end mills is biased toward larger sizes, because people thrash the smaller ones, and the cutters that are provided are those Harbor Freight box sets. This seems like false economy, since the sets seem to be primarily purchased for the smaller cutters which are quickly thrashed. I bought 25 end mills at a garage sale for $40. I was really afraid of the quality, but once I got stuck with that sad, lonely 5/16" Harbor Freight cutter, it was clear that almost anything else was better. The garage sale end mills were all good USA brands, but some were dull or chipped. Others were new. Those Ebay lots might also be better than Harbor Freight remnants. It seems that it would be much more economical to go with used lots than those Harbor Freight wooden boxes. This is not a complaint about their quality. It is just an observation on the usage model.

Another thing the instructor brought up is your opportunity cost. Even if you baby an end mill, it should only last for a maximum of 6 hours of cutting. If you go in to the Techshop 4 times in one month, that is $30 per visit. It is worth buying one for that visit, even at new price.
 
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