Cutting circular slots in mild steel

Hi guys,

Title should have read Circular

I'm now making two off MS plates to house the bearings for my lathe headstock. The only method I have to achieve this is to clamp a plate to my rotary table and use and end mill to progress down to 16mm and almost out to full diameter. I then creep outward on the final interference diameter for the bearing outer. This creates a circular slot because the centre section is the only way I can bolt the plate to the RT.

The plates are 20mm thick and I'm cutting down to a shoulder 16mm deep for the bearing to pull in against.

I've done one plate already and my 8mm, 4 flute end mill is getting rather blunt. At the moment I don't have a cutter-grinder.

Being a relative beginner in machining I was wondering would this be better done using a 2 flute slot drill or roughing mill and finish with a 4 flute end mill?

Cheers,
Ed.

Edited By Ed Duffner on 20/05/2014 18:35:05

Hi Ed,

if your initial cut is a circular slot I would use a slot drill (2 flute). If making the slot wider an end mill might be better. Your cutters going blunt when milling steel is something I have experienced too, there can be several causes. Either grind/sharpern the milling cutters or get new ones.

Thor

Thanks Thor, yeah I'm thinking about getting another cutter hence the question about which might be best for slot work. If it was a straight slot I'd probably go for a 2 flute slot drill, but I was unsure if a circular slot required a different approach.

How big is the plate? can you do it in the lathe its basically a similar method to Trepanning where we have had a couple of recent threads.

Ignor this if the lathe is out of action until the plates are made.

Edited By JasonB on 20/05/2014 19:45:05

Hi Ed and guys
I would use a slot drill for rough slotting then finish using an end mill . if the spindle is zeroed to the centre of the rotary table and dials set. Move Y axis to radius required less 1/2 cutter (R minus ) less say about 10 thou . run round dont climb mill . as it may snatch when you are milling round the slot . check size for fit may be 20 thou small repeat to finish . Leave approx the same on the bottom . you can then remove the centre metal not required clamping direct on milling table . the CNC guys would have a canned cycle for this job What mill are you using ?
Nobby

Thank you Jason and Nobby, the lathe is out of action, this is part of it I'm rebuilding. I have two 125 x 100 x 20mm plates to make the faces, it'll be a bit like the Sieg headstock casting with pressed in taper-roller bearings but only the ends where the bearings are. The plates will be bolted to a base plate on the lathe.

Nobby, you have described what I'm trying to achieve very well. I was a bit coy on the first plate and left about 1.5mm in from the edge as I didn't want to get too close. I keep forgetting that 1.5mm is actually a very large distance in engineering terms I am doing something similar to CNC where they spiral the cut down about 0.2mm for each rotation, but manually in the first 15mm or so of each pass.

I will get a 2 flute slot drill to finish this job off. I am using the Warco WM-16 milling machine.

Here's the idea. The left plate is as clamped in the mill and the finished item on the right.

Thanks again,
Ed.

I managed to find an imperial slot drill in my Dad's stash of tooling so can continue today.

Thank you to whoever changed the title spelling, JasonB ?

Perhaps a silly question but why can't you rough out and use a boring head to get the bearing diameters ?

Hi John, no boring bar, not much money at the moment. I want to eventually make a boring bar as per Harold Hall's design in the Milling Book. ...but I need a lathe to do it.