Cutting circular slots in mild steel

[Ed DuffnerParticipant @edduffner79357]

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

[Ed DuffnerParticipant @edduffner79357]

Which cutter(s) to use?

[Thor 🇳🇴Participant @thor]

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

[Ed DuffnerParticipant @edduffner79357]

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.

[JasonBModerator @jasonb]

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

[NobbyParticipant @nobby]

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

[Ed DuffnerParticipant @edduffner79357]

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.

[Ed DuffnerParticipant @edduffner79357]

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 ?

[John Stevenson 1Participant @johnstevenson1]

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

[Ed DuffnerParticipant @edduffner79357]

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.

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