Simple(?) Milling Question

[Chris VParticipant @chrisv]

I have an Amolco mill but not undertaken any milling as yet. I have been reading Jasons articles on Milling for Beginners from which I have learnt a lot, so thank you for that.

I would like to make some hand knurling tool holders for some 1/4" wide rope knurling wheels I have.

I think the material will be 14mm square mild steel, and partly turned. At the business end I will need an open end slot, 1/4" wide x 1/2" long.

Drilling a hole through and cutting the rest away with 2 cuts of a slitting saw I think may well result in a less than perfect slot.

I could use a slot drill if I can find one 1/4" wide.

Or as I was initially thinking a 1/4" horizontal side & face cutter in an arbour.

Which would be your recommended method please, and HSS ok or do I need to look for carbide tipped?

Many thanks in advance,

Chris.

[Chris VParticipant @chrisv]

How best to cut an open ended slot in mild steel

[Anonymous]

I've just done this for a clevis on my regulator, bottom middle:

Sadly I don't have a picture of the slot machining as I didn't think it merited one. I cut the slot with the steel bar vertical in the machine vice. I used a 6mm carbide endmill. First cuts were through the middle of the slot going 2.5mm deep per pass. I then shaved one side full depth (20mm) to get the side to the correct thickness, and then the other side to get the slot the correct width. For a hand knurling holder it wouldn't matter if the slot wasn't exactly central.

I considered using a 1/4" S&F cutter, but it was too much of a faff to set it up. That would have been on a large horizontal mill. I wouldn't consider using the S&F cutter on my vertical (Bridgeport) mill; it simply isn't rigid enough.

Andrew

[Clive Brown 1Participant @clivebrown1]

All those methods will potentially work butI think that I'd try a 6mm end-mill, or slot-drill and then take a shaving off the side to open out to 1/4".

A 1/4" S&F cutter on mild steel is asking quite a lot for a light mill.

[old martParticipant @oldmart]

It would be best if you ended up with a smaller milling cutter and cut each side bit by bit to get an accurate slot.

[EmgeeParticipant @emgee]

Hi Chris

I believe you will be best served with a 6mm slot drill, you can lessen the load by drilling a 6mm hole at the end of the slot, and after cutting to full depth by about 4 passes move the tool over to finish 1 side with a full depth finishing cut then moving again to the other side to cut to the 1/4" width required.

A 1/4" side and face cutter would no doubt be the right tool in a fairly heavy horizontal mill on a supported arbor, but I think your setup may struggle a bit with such a load.

Emgee

Just come back to the topic and see I am repeating what has been said, never mind will type less next time. !!!!

Edited By Emgee on 07/06/2020 16:09:08

[Chris VParticipant @chrisv]

Ok thank you, so a S&F cutter it seems is a no go on a light weight machine.

My lengths of steel will be approx 6" long so I cannot cut the slot with the material held vertically.

So if I hold it in my milling vice with say 5/8" hanging out the end should I try to cut the full depth ie 9/16" feeding slowly to make full use of the cutter, or multiple cuts each one a little deeper?

Or in other words, I think Emgee has just nailed the answer for me!

Thank you all!

Chris.

[JasonBModerator @jasonb]

If you have the head room than the work can be clamped to an angle plate or block of metal so it can be cut vertically rather than having a lot sticking up out of the vice.

If you do need to cut it horizontal then 1.5 – 2.0mm deep per pass would be about right for the light machine.

Drill the cross hole for the pin first.

[Chris VParticipant @chrisv]

Thank you yes drilling the hole first is a good point.

I don't think I have the head room, but if I did have would the suggestion be that I advance the job upwards and outwards between cuts? That dosen't seem right but I'm asking as I don't know, or is it that a light weight mill will be more rigid cutting it that way?

Also HSS ok?

Many thanks

Chris.

[Martin ConnellyParticipant @martinconnelly55370]

Feeding slowly is not a good idea. The tool needs to cut. You will be better doing a number of shallow passes. Start off with good habits, learn about speeds and feeds and use them as a starting point. Once you have things going reasonably well you can vary the parameters to suit your machine.

Thread on speeds and feeds

Online speeds and feeds calculator

Martin C

Online calculator link added.

Edited By Martin Connelly on 07/06/2020 16:42:46

[JasonBModerator @jasonb]

Posted by Chris V on 07/06/2020 16:26:28:

I don't think I have the head room, but if I did have would the suggestion be that I advance the job upwards and outwards between cuts? That dosen't seem right but I'm asking as I don't know, or is it that a light weight mill will be more rigid cutting it that way?

Also HSS ok?

If you have the knee type then raise the table for each pass, if the fixed table or attachment then lower the quill down for each pass. Work will stay locked centrally which would usually be the Y-axis and fed along the X-axis

Yes HSS will be fine, I'd go with a 3-flute myself as they are more versatile in the long run

[Chris VParticipant @chrisv]

Brilliant as always, thank you Martin Ive printed out the speed chart.

Thanks so much Jason, I will take a look at what Arc have to offer!

Cheers

Chris.

[duncan webster 1Participant @duncanwebster1]

Does the slot have to be square ended, if not you can machine it with the bar horizontal. Drill a say 3/16" hole at the end, then repeatedly plunge in with a 6mm slot drill and cut towards the open end, then a skim off each side to get the right width.

If it does actually need to be square ended, do as above then square it off with a file

Edited By duncan webster on 07/06/2020 17:40:35

[Martin ConnellyParticipant @martinconnelly55370]

Another thing a beginner to milling needs to be aware of is the difference between climb and conventional milling.

MEW article

Martin C

[Chris VParticipant @chrisv]

Thank you Duncan, no the slot end can be round and it would look better for it I think, as yet undecided.

So you suggest like chain drilling, but maybe overlapping each hole, then cleaning up with a skim as you suggest?

Thanks Martin, yes I'm aware of this as for work I have used a wood router many times. That's not to say I fully understand it so shall certainly read the link you sent!

If my metal stock is held horizontal will I be better off with the end I'm cutting overhanging the end of the vice so I can cut right through, or support on parallels within the vice.

I'm thinking if its hanging out the side of the vice the thin sides may spread when cutting resulting in an uneven width slot,

Likewise if fully supported within the vice maybe the jaws could push the thin sides inwards?

That said I'm leaning towards having it fully supported but very greatfull to hear from those with experience!

Chris.

[JasonBModerator @jasonb]

I'd put it on parallels to bring the top of the work approx level with the top of the vice jaws, OK to have all the length within the jaws as the unmachined part will stop any chance of things closing up.

[Chris VParticipant @chrisv]

Thank you Jason, guess I best look at parallels too then (-:

Chris.

[JasonBModerator @jasonb]

Anything will do that is reasonably parallel, a piece of flat/square bar, lathe tool. etc

[Chris VParticipant @chrisv]

Oh yes, hadn't thought of that!

Being a past woodworker…what about hardwood such as oak?

Chris.

[JasonBModerator @jasonb]

should do

[Martin ConnellyParticipant @martinconnelly55370]

For your proposed use the slot is just clearance. In this case it will not matter if the bar is not quite horizontal in the vice so anything that holds it reasonably horizontal and close to the top of the jaws will be fine.

Martin C

[duncan webster 1Participant @duncanwebster1]

For a 6mm cutter I'd just drill one hole at the inboard end and machine the rest with a slot drill, but you could chain drill, or even saw out the excess. Good idea to put it on parallels inside the jaws, but put something sacrificial between the job and the parallel, or use wood

[Chris VParticipant @chrisv]

Thank you, yes I'll likely go for wood in this instance.

Next question having just looked on Arc's website:

My draw bar is 3/8" Whitworth. For my Mill I have both 6mm & 1/4" Myford type collets that fit into the 2MT spindle.

I could buy a 1/4" cutter and fit it directly into the Myford collet in the spindle, so minimum projection which I do know is what I should aim for.

Or, I could buy a Weldon cutter holder for 1/4" cutter with 3/8" draw bar thread.

OR, should I get the 6mm cutter and fit it in the Myford Collet, and NOT use a Weldon as these only come with

10mm draw bar thread?

Thanks

Chris.

[Martin ConnellyParticipant @martinconnelly55370]

Weldon collets cause runout of the tool. The tool goes into an oversize hole and is pushed to one side. This may not matter so much in large diameter roughing tools but is something to avoid with small tools. I don't know what collets you have but if you want to hold the cutter away from the spindle nose you could get something like an ER11 collet chuck on a 12mm parallel shank and cut the shank to a length that suits your needs. Put this into a 12mm Myford style collet. You could also consider an ER16/MT2 collet chuck. ER collets will hold the 6mm cutter with far less runout than a Weldon holder.

Martin C

[JasonBModerator @jasonb]

I'd go with their Premium cutters so that means having to use 6mm and hold that in your collet

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