Milling Insert Screws

The fastening screws for the 1604 size inserts are 4mm whereas the 1003 inserts are 2.5mm. Does anyone else feel that the smaller size might be fine for lathe tools but is pushing the envelope a little too far for milling inserts under heavy intermittent loads ?

I think most insert suppliers suggest a smaller depth of cut (vertical) for the smaller inserts typically 1-6mm compared to 1-14mm for the larger so you should not be taking as big a cut with the small ones and therefore less load on the screws. Also if you put a CSK 4mm hole in a small insert it's likely to be weaker due to less distance to the edge.

The screw is there to stop the insert falling out. It shouldn't be taking any significant cutting forces. The cutting force vector should be pushing the insert into the pocket, so the holder takes the forces, not the screw.

Andrew

I have managed to snap an M2.5 insert screw when using a 2 insert Ø16 end mill at a depth of 7.5mm in steel. It was an original and probably not the best quality as the head was rapidly showing signs of damage in use. I swapped out the other screw as well when I replaced it. Based on Jason's post I was probably pushing it a bit too far on depth.

I thought I was going to have a job getting the remains out but as soon as I touched it with a small engraving tool in a Dremel it spun out.

Martin C

I made a fly cutter that uses RCGT06 cutters for alloy. These take M2.5 Torx screws and I’ve not had one fail so far. I’ve been using the tool for several years. The Taiwanese made Torx insert screws I’ve bought on eBay seem to be good quality.

I have been making a mill boring head bar in 1/2" diameter Densimet to use DCMT 07 inserts. It will be long enough to reach 2 1/2". The screws which hold the inserts are also 2.5mm. The threading is the last operation as the hole for the screw has to be offset slightly to hold the insert tightly in its pocket. I used the first tap in the drill chuck part way, but as it is difficult to turn in the Tom Senior, I opted to finish by hand. I managed to break the tap and spent some time drilling the tap remains with 2mm solid carbide drills and endmills. The last part came out with a little persuasion with a micro drift and a toffee hammer. Tomorrow I will be attempting to tap the remaining length of thread. The bar will be the first of several intended to be superior to those aweful brazed carbide things that the heads come with.

I also have milling cutters with APHT 11 which have the smaller size screws which match the insert size and only an ideot would take the same cuts as the APHT 16 inserted cutters are capable of. As Andrew says, the insert is supported and is not totally reliant on the screw.

I've got Glanze versions that take the DCMT inserts and often use the boring head for arcs rather than full circles and not had problems. Also run CCMT and CCGT 06 lathe tools in a flycutter again no problems.

I have three boring head tools which take the simple single sided triangular inserts, but they are nowhere near long enough to reach 2 1/2" They use a clamping screw about 5mm size. My smallest inserted tooling is a Garant 6mm solid carbide boring bar for lathes which uses 1.8mm screws.