I have done similar on the lathe upto 3/16" wide and it takes a lot of force to push the tool through. If doing it on a mill I would suggest doing it first with a 4mm wide tool and then again with a 6mm tool to final width.

I have also used a drill press to frive keyway broaches and 1/8" width is the most load I would want to subject the rack to.

These four are 3/16" wide, 1" long through steel done one thou at a time on the lathe

Reduce the cutting loads by fitting a bore filling spigot so the bulk of the metal can be drilled out. 5 mm would be a good start. I'd probably go 5.5 but having done this a time or three have a reasonable handle on how to get close without going over. Take out the round corners with a file. A few strokes down the side too won't hurt. Finish with the slotting tool in lathe or mill drill according to preference. Most of the cuts will just be nibbling down the sides. Ideally there will only be three or five full width ones as you get to the bottom. if there is a significant amount of material left to remove a file is faster and kinder to the machines. Your slotting tool is finisher to get the shape right and direction straight not a bulk remover.

Recieved wisdom is that a lathe is stronger and more accurate at this sort of job but I suspect there isn't that much in it between your Myford and Mill Drill. My machines are much heftier so I don't have feel for the strength of yours. If you anticipate doing much more of this sort of work take time out to make a proper slotting tool. In the early days of MEW a sound design for such was published which I considered making but rejected the idea as I didn't have materials to hand and anyway very rarely cut a keyway slot so probably would have got the use to justify the making. How wrong can you be. Over a couple of decades very rarely has still added up to more than enough to justify the making.

Clive

Given your machinery – then the drill and file route may be a good one for you to explore Kenneth. however I also thik your idea of using the tool side ways in the lathe is also well worth considering. As to the force required,, whilst I don't disagree that the force required could be quite large with a 6mm tool but why not use a thinner tool and rotate the work slightly to either side to get near the required width and then finish to size with the 6mm tool. I've not tried this but I don't see why it wouldn't work..?

Like John I also have Shaper but personally I could set one up and do this work a lot quicker than the drill and file route – but then unlike the old timers my filing is pretty rubbish. So everyone has their own preferences and available skills. So several solutions open to you and if this is a once in a blue moon need – then a bit of extra time here or there is not that important. Do it the ay you feel most comforatable with and that gets the result you want.

Regards,

IanT

Edited By IanT on 28/05/2016 10:20:25

The last time I had any slotting to do, was to make a couple of externally splined shafts for a gear shift on the Ducati. It was a pointed tool, so less loading than your 6mm slot, but there are suggestions above to reduce the forces involved.

In my case I cut the splines from the top slide, rather than risking damaging anything connected with the saddle.

I removed the top slide's feed screw, complete with end plate (Super 7). I then replaced it with a double lever arrangement, on a home made end plate, pivoting on a stub, bolted to the Tee slots on the cross slide. The saddle was locked in the normal way for parting off. This way I could use the top slide as a lever actuated slotting attachment, with a cutting tool horizontally in the toolpost without risking the rack or half nuts.

It's much the same arrangement as a lever operated tailstock drilling conversion, but on the topslide.

From memory, I ground the tool with lots of top rake, and angled it to the shaft, such that if I took too deep a cut, it would push the tool out of the way, rather than digging in to the workpiece.

Indexing was done via another quick lash up. A basic gear train from the spindle, a detent, and a length of twine wrapped round the chuck with a bob weight hanging off it.

Doing it this way also allows splines or slots to be cut on a tapered workpiece.

If I were to have this to do on a regular basis, I might even buy a spare top slide to use as a ready made slotting attachment. The gizmo I made was quite crude, but worked well enough for a one off job, as the precision bits had already been made by Myford.

Edited By peak4 on 28/05/2016 10:55:39

John

Did you mean the Polikey system from Poliangolar. Not a milling cutter. Still a basic square section shaping / slotting tool. Clever part is that its arranged to pivot out from the side of a relatively slender shaft by turning a handwheel. A bobbin the same diameter as the parent hole fits on the side of the main shaft to provide support directly under the cutter. Looks to be a neat idea but probably more for 12" to the foot scale work than models. Looking at the video I get the impression a tool capable of 1/8" keyway in 3/8" bore is about as small as could be made. Not easy and not something I'd care to do, 1/4" keyway in 1" bore or bigger being more my speed.

I seem to recall something covering a similar principle in either ME or MEW some years back. As I recall it that article looked at providing an adjustable cutter in a rather larger shaft to reduce spring. Don't recall anything about a support bobbin tho'. Idea seemed to be about using the largest possible shaft althoug obviously it would be supported if the shaft filled the parent bore.

I've often wondered if there is any way of making an expanding sleeve or simple pivoting arm support to fit onto a simple round boring bar to support the tool. In principle it could be screw driven so the expansion matched successive cuts. In practical I never saw any sensible way of making something useable. Especially given that it needed to be small.

Clive

PS Tried a different search and turned up the rotary system John was talking about.  Impressive but the cutter is clearly pretty special and the whole system looks expensive.  Fundamentaly, like rotary broaching, yet another offsping of the wobble drill process used to drill square and polygon holes.  First time round Google cleary got confused as the compay is Poliangolar and the make both the Poliangolar rotary system and the simpler Polikey broacing system.

Edited By Clive Foster on 28/05/2016 18:25:58

Hi Clive,

After I posted the poliangolar (SP?) idea I went and looked again at the url I had stored and it was no longer active. The new Poliangolar system is completely different, more of an eccentric broaching system.

The one I saw, they even had a video of a guy sitting at a drill press cutting keyways in change gears!, it was a round spigot with a tiny side and face cutter poking out of the side. The drill chuck drove the cutter by a helical shaft, like a worm wheel, and it cut pretty quickly. No idea where the link is now but it was a very clever beast. Seems they had been around a long time and it was an American company. Another mystery!

Was this the one, John ?

**LINK**

… Looks promising

MichaelG.

IanT's recollection of a published design for similar adjustable, single tooth, key-way broach pretty much accords with my own. I think the author wanted to use a normal multi-tooth push broach on component having an internal shoulder (?) preventing the broach from being pushed right through. The adjustable device let him cut the keyway up to the shoulder. My recollection is that he started out trying to adjust the depth of cut by stacking shims in the slotted bore filler normally used to support multi-tooth broaches which didn't turn out too well so he figured out an adjustable one still running in the support bush.

One wonders if its practical to make a similar system doing without the slotted bush having a support finger opposite the cutter and moved by the same adjuster. I imagine the ends and sides of the support finger would need to be cunningly curved to give smooth operation over a reasonable size range. Probably more practical if the bore is plugged and a starter hole drilled first. Especially in smaller sizes. Tricky part appears to be devising an adjustment system that doesn't rely on a small screw right at the business end.

Clive.

IanT is this what you are thinking of, Its come up a couple of times on teh forum before

Could use a round bush with an off center round hole if you need to use in a larger hole