Cutting small tee slot in steel

[MattKParticipant @mattk47317]

Hi,

I want to cut a small t sot in a piece of steel. I have milled the plain slot but can't find a tool small enough to cut the ears. Any ideas how I might be able to do this or where I could find a tool to do it. I have cut this in my Myford S7 on a cross slide as I don't yet own a mill. Thanks,

Matt

[MattKParticipant @mattk47317]

[NJHParticipant @njh]

Matt

Is this a "T" slot to match those on your Myford? If so you will find one here

( There may well be other sources)

regards

Norman

[David LittlewoodParticipant @davidlittlewood51847]

Matt,

Might help if you told us the size of the slot you want….

David

[Ady1Participant @ady1]

He probbly wants a myford sized slot, or thereabouts

I tried it at high speed on my M series and it was too dodgy, too much heat and chatter, too much chance of a broken t-slot cutter

 

However, with the backgear engaged, and some patience, you can mill your way through solid steel.

 

You will need to practice first.

Mill some steel away from the surface of a lump of steel using a t slot cutter, listen to the job and take your time

If you dive straight into a t slot job with no experience you will probably fail, quite spectacularly.

One of the big issues with a woodruff cutter is that the further it is away from the centreline, the more the torque drops away, and this happens fast when milling steel

You don't even notice this problem with a slot drill

Edited By Ady1 on 05/07/2012 00:36:51

[Ady1Participant @ady1]

and the cutter purposely made for the job from an 8mm Slot drill

Miles easier than using a woodruff cutter, easier to resharpen and probably cheaper too

Any chance of a picture showing us all how you ground the top of the cutter flutes please Graham?

[NJHParticipant @njh]

Ady

I'm a bit puzzled by your statement :- " One of the big issues with a woodruff cutter is that the further it is away from the centreline, the more the torque drops away" – I guess I'm being a bit thick here ( not that unusual I grant!) but could you explain a bit further please.

N

[MattKParticipant @mattk47317]

Hi,

Sorry, I posted an inline picture which shows up to me (even a day later) but obviously not to anyone else. The slot is similar to the sizes discussed it about 8mm deep and 10.5mm wide at the widest pointnarrowing down to around 6mm. I have slotted it to 6mm. It just needs the ears cutting and they are around 6mm deep.

Graham, I had seen a cut down slot drill before but not looking exactly like this. How do you do this? Do you need to rig up a grinder on your toolpost and spin the cutter up in the chuck?

Ady1 – thanks for the advice about the backgear, I was going to ask about speeds so I guess pretty slow. I did look at a woodruff cutter but was concerned whether there would be enough clearance on the shank of the tool

Matt

[Ady1Participant @ady1]

One of the big issues with a woodruff cutter is that the further it is away from the centreline… but could you explain a bit further please

—-

The easiest explanation (theoretically speaking) is if you put a faceplate onto your lathe and with the backgear engaged try and stop it turning with your hand

You will always try and stop it turning by grabbing at the outside edge of the faceplate because the torque in the centre zone is massive compared to the outer edge and your hand would grab the front, back and edge part of the faceplate to maximise your leverage

 

Unfortunately, on a woodruff cutter it's the same situation, it's cutting the top, the bottom, AND the front face at the same time, so it's working on three faces, two of which are depth cuts in solid steel so a small increase in diameter creates a much tougher job for a hobby lathe to overcome

A perfectly sharpened tool makes things better but a general hobbyist will struggle to resharpen a multi toothed woodruff cutter properly, a two flute cutter would be a lot easier

 

edit

I only found out about this because I got a job lot of woodruffs from fleabay and ran into some serious issues with only a slight difference in cutter size with my myford M series hobby lathe

A 12mm slot drill cut is a doddle on the backgear but a 12mm t-slot cut was an entirely different ballgame and a bit of a hail mary job

It's probably a stiffness issue which wouldn't be noticed on a bigger more powerful machine

Edited By Ady1 on 06/07/2012 01:31:07

[John OlsenParticipant @johnolsen79199]

There is actually a difference between a T-slot cutter and a Woodruffe cutter, and cutting T slots is likely to go a lot better if you use the right one. Woodruffe cutters are designed for cutting slots for Woodruffe keys, logically enough, and they don't have side clearance. T slot cutters do have side clearance. So make sure you are using the right type of cutter. The smallest t slots I have cut are 1/8 inchcross the top of the T, with a 1/16" slot. These are on my 1/8 scale Alba shaper, and are really only for show.

The other way I have cut T slots is on the shaper, the nice thing there is that you can make your own cutters very cheaply by brazing a bit of HSS onto a mild steel shank. You need left and right hand, and if you want to undercut the T by more than half the width of the slot you will need to make two cutters. But usually the proportions with the T arm being half the slot width is fine.

John

[NJHParticipant @njh]

Matt

I have dug through some old projects, one of which was George Thomas' small rotary table which I made many years ago. ( You can see this if you look in my photos under GHT rotary table) This was supposed to have 4 "T" slots cut in it but, due to  lack of a cutter at the time, I just tapped a few holes for studs to fix the work to the table. Now in his book " The Model Engineers Workshop Manual" George describes how to cut the "T" slots. Whilst he recommends using a vertical mill he describes how he did this on his S7 lathe. The slot is about the size of the one you propose, his initial cut was with a 1/4" slot drill followed by the "T" slot cutter "running at about 400rpm with the use of plenty of soluble oil to wash away the chips"

I found this a fascinating project and George "held my hand" all the way through. I remember that the prospect of cutting curved AND dovetailed stops was beyond my imagination but by following his instructions all turned out well.

If you wish to go along this path just send me a PM and I will copy some of the instructions to you.

Regards

Norman

Edited By NJH on 06/07/2012 20:35:24

[Sub MandrelParticipant @submandrel]

My T-slot cutter is about 3/4" diameter, but as well as having clearance it is gashed like a rippa mill.

With the central groove pre-milled out, I had no problem driving this large cutter on my mini-lathe.

Neil

[David LittlewoodParticipant @davidlittlewood51847]

One thing which helps is to take the initial slot just a couple of thou lower then the lateral T-slot is intended to be; this means the T-cutter does not have quite so much work to do, and does not affect the strength of the finished slot.

David

[Ady1Participant @ady1]

Thanks for that Graham, 2 flutes are definitely the way to go for an amateur IMO

Thats a nice looking grinder btw

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