Slitting saw or t slot cutter ?

[picclock]

Hi

I need to cut a 4mm  wide slot onto the outside edge of a 108mm x 10mm mild steel disc. I only have a small lathe which tends to chatter with this kind of thing, so i thought I would do them on the mill with the rotary table. Not having a 4mm slitting saw, i stacked 4x1mm ones together. The finish at the bottom of the slot was rubbish, and it took quite a long time to do. I'd left the slot a bit shallow so I was able to tidy up a bit on the lathe. So I was wondering if it would be worth investing in a T slot cutter which can be bought for 4mm slots. The slot depth is only 2.1mm so that shouldn't be an issue. I need to do a few of these so what is the typical life of such a tool ?  The other approach which I'm a bit reluctant to consider, is to stand the rotary table on its side and have at it with a slot drill (2 flute endmill). But I have a less than stellar track record with the small ones, and as I only have a 6" rotary table it will have to be a very long slot drill - so probably not a good approach.

My current plan is to purchase two more 2mm slitting saws and stack them as before, but if its worth trying a T slot cutter I'll give it a go.

Best Regards

picclock

[wheeltapper]

It depends on what you call a small lathe.
I would do it in the lathe with a narrow parting tool ( 2mm say) and take two bites. if that chatters try a thinner tool.

Roy.

[Fergus OMore]

One drill ( ?2mm) to open the hole- finish with a hacksaw with 2 blades together or a warding file.
 or drill out corners of would be slot- finish as before

or if push comes to shove-why not  make a  baby chisel out of a hex key or a drill or a bit of silver steel. Sharpen it up like a cow mouth chisel and away you go. Use a toffee hammer or =, in my case, my wife's hammer for extracting broken teeth.

Plenty of information on 'graving tools' for making( laugh) graven images.

[kwackers]

If you can't use a parting tool I've had a fair bit of success making a suitable tool using a square of mild steel as a tool carrier and grinding a broken drill of the right diameter into the cutting tool.
This is simply mounted in a hole drilled at right angles in the carrier and fixed with a grub screw. Leave just enough sticking out to reach the depth you need and you shouldn't have too many problems. (Works well for internal grooves too)

[picclock]

Hi Roy

I have three parting tools 2.2mm and downward to 1.45 mm which I have tried. Its only a 7x14 lathe so its fairly limited. The issue occurs because the cross slide and tool holder are outside of the ways at this diameter, therefore the front way acts a a pivot for the cross slide. I can get away with turning metal as long as I am careful, but using a parting tool where higher forces are incurred causes issues. Parting at smaller diameters, say 2" is no problem but with a part over 4" its generally doesn't seem possible.

@ Fergus OMore
The slot is to be cut round the circumference of the disc (the outside edge) and goes all the way round it.

Best Regards

picclock

[andyf]

Any chance of getting a clamp on the top of the saddle, where it's exposed behind the cross slide, and the underside of the rear bedway, to hold the saddle down so it can't pivot?

Actually, studying your last pic, I see you already have a clamp hanging down between the ways. I'm surprised that isn't enough, but obviously it's not.

Andy

[Rob.Wilson]

Hi picclock

If it were me I would have a heavy centre drilled into the end of the mandrel , bring the tail stock up for support , use a 2mm parting tool upside down and run the lathe in reverse ,slowest speed 



Rob

[lordedmond]

Use a  right angle tool like a boring bar with the shank parallel to the lathe bed , with the tool holder turned round, and the tool in the slot nearest to you that way the tool post would be more over the bed


Stuart

[Fergus OMore]

Hi picclock

If it were me I would have a heavy centre drilled into the end of the mandrel , bring the tail stock up for support , use a 2mm parting tool upside down and run the lathe in reverse ,slowest speed 



Rob

I sort of agree except that a rear upside down parting tool with a hss blade mounted at 7Degrees will literally carve through  the block at 200 revs. in forward gear. Rob is absolutely right on adding as much rigidity with a sturdy centre( a revolving one would be my choice).  This, after all is GHT's rotary table 'words and music' and Chaddocks for his Quorn. GHT cut a tee groove and I did mine in three cuts with home made offset ground parting tools.

Nice!

[Pete W.]

Hi Roy

SNIP

The issue occurs because the cross slide and tool holder are outside of the ways at this diameter, therefore the front way acts a a pivot for the cross slide. I can get away with turning metal as long as I am careful, but using a parting tool where higher forces are incurred causes issues. Parting at smaller diameters, say 2" is no problem but with a part over 4" its generally doesn't seem possible.

SNIP

Best Regards

picclock

SNIP

Hi there,

If the trouble is that half the saddle is over the bed gap and hence not supported by the bed ways, can't you mount the job on a longer mandrel with one end in the chuck and the other supported by the tail-stock centre?  Would you then have enough clearance over the cross-slide and/or the saddle?

[Fergus OMore]

I think that the reference of rear parting tools comes from Ian Bradley's original casting for his ML7. George Thomas took it up on his machine and after a series of experiments settled for inclining it at 7 degrees with a cutting angle of 140 degrees inclusive.  GHT then angled the front cutting edge to a positive 140 degrees and a negative vee of 140 degrees. ground into his pair of hss blades. I noticed that a Ken McIntosh modified this to a simpler casting and others started to use broken hacksaw and machine hacksaw blades.

Someone found that he couldn't quite achieve the top negative vee kerf and settled for a round concave shape.

It's all very simple really but the result is that the ribbon of swarf is narrowed and does not bind and seize and snap the tool- at fairly exciting speeds in forward motion.

OK, I did mine to fit a then rickety ML7- long past its sell by date. I swopped it onto a 9180 and it is now on a early Super 7 B- still with the original Eclipse blade.

Whilst I have a Quorn, A Kennet, a Stent and a Clarkson 1 which will perform far fancier shapes, I started to merely straight grind the face on the tool. I've hacked my way through some very nasty welds and so on with a mixture of metals. As I said earlier, I've made the GHT small rotary table and the Quorn's rotating tool holder.

Perhaps the little tool post is the best bit of my kit and still on a somewhat weak saddle. Super7 saddles are traditionally weak and wobbly affairs- with bloody big holes in them.-designed in them.

That's my take

[doubleboost]

I think that the reference of rear parting tools comes from Ian Bradley's original casting for his ML7. George Thomas took it up on his machine and after a series of experiments settled for inclining it at 7 degrees with a cutting angle of 140 degrees inclusive.  GHT then angled the front cutting edge to a positive 140 degrees and a negative vee of 140 degrees. ground into his pair of hss blades. I noticed that a Ken McIntosh modified this to a simpler casting and others started to use broken hacksaw and machine hacksaw blades.

Someone found that he couldn't quite achieve the top negative vee kerf and settled for a round concave shape.

It's all very simple really but the result is that the ribbon of swarf is narrowed and does not bind and seize and snap the tool- at fairly exciting speeds in forward motion.

OK, I did mine to fit a then rickety ML7- long past its sell by date. I swopped it onto a 9180 and it is now on a early Super 7 B- still with the original Eclipse blade.

Whilst I have a Quorn, A Kennet, a Stent and a Clarkson 1 which will perform far fancier shapes, I started to merely straight grind the face on the tool. I've hacked my way through some very nasty welds and so on with a mixture of metals. As I said earlier, I've made the GHT small rotary table and the Quorn's rotating tool holder.

Perhaps the little tool post is the best bit of my kit and still on a somewhat weak saddle. Super7 saddles are traditionally weak and wobbly affairs- with bloody big holes in them.-designed in them.

That's my take

Any chance of a picture or 2 of your tool grinders
John

[vtsteam]

Maybe it's an illusion, but If I lay a straightedge across the photo of the face view your parting tool looks above the centerline.

Tubal Cain had a number of suggestions for assisting parting tool operations -- tough to describe all in words but I'll try.

First of all a fish tail shaped grind in plan view of the parting tool end.

Second, a packing strip of steel placed under the parting tool as a support. This strip had a rectangular leg -- looking like a flag hanging down near the tip. It was in contact with both the lathe saddle and the strip -- brazed to the strip. Thus the parting tool had essentially tangential support.

He also had an alternate toolpost -- basically a huge blob of cast iron he called "the Gibraltar" -- but that's beyond the scope of this job.

[picclock]

So although the info on the lathe changes are interesting no one has answered the original question as to which is best for cutting the slots on the mill,  a slitting saw or a T slot cutter.

Other slightly odd thing is I can turn the metal disc on the lathe with no real problems, but the chattering issue is always there with the parting tool with these larger sizes. I have tapered roller bearings on the headstock which I have just checked by hand for deflection, which gives +- 2 thou with strong hand pressure - is this excessive ? I have no idea what sort of movement a normal lathe spindle would have.   

Re the tooling height. The height in the picture is correct but I tried varying a mm either way to no real effect.

Best Regards

picclock

[vtsteam]

Kinda hard to say what's "best" about almost anything, particularly without the experience of a person's workshop equipment, the precise cutting tool contemplated its condition, your tendencies in feeds and speeds and your expectations of finish and ease of use.

I imagine you got a lot of lathe responses because people thought a turning solution was better for this piece than a T slot cutter or a slitting saw. But nobody knew for sure under your own conditions, any better than you did. So, one solution is try both on some scrap, and report back.

The deflection in your spindle might be play or deflection, you didn't say whether there was a "clunk" to get there.

If play, then that can be remedied, if deflection, unscrew your chuck, screw on a faceplate and bolt your piece to it, wide face toward the headstock. You'll remove a lot of overhang that way.

[lordedmond]

Picclock

to answer your first question it depends on the job the material and the position of the slot

they will both give you a slot , but IMHO it all depends on the job in hand


as to your lathe you say + - 0.002 inches thats way to much nip up the pre load a bit ( not at the current temps in the UK ) and run the lathe at full speed for 10 mins shut down and feel the bearing housing if it very cool the another small nip up of the pre load until after a 10 min run at full speed the housings are  just warm ( in the temps we have at the mo aim for slightly warmer than the other end of the bed )

Stuart

[vtsteam]

Also, if you do want to try to mill it, why not grind an end mill to the profile you want rather than buy a tee slot cutter? You're cutting a shallow groove. Just relieve the upper flutes a little past that depth and leave the lower portion as is for cutting the groove. It's likely to be stronger than a tee slot cutter, and cheaper, and you don't have to send for it.

[tekfab]

What kind of milling machine do you have ? I'm having trouble trying to imagine the problem you describe if you tried to mill the slot with a slot drill.
The slitting saw idea sounds like no no. That job can be done easily on a lathe without a lot of difficulty .

Mike

[PekkaNF]

ref#1 post. I would imagine that a stack of four slitting saws would clog pretty fast. I would try 4 mm slitting saw if available, because that would be a whole lot rigid and you allready have all the bits for that setup.

I never had that small T-slot cutter, but I think that slitting saw wins over: Slitting saw is more rigid and probably will cut longer and probably cheaper too.

HSS Slitting saws must be run incredibly slow. Just yesterday I cut one car gearbox/coupling housing with about 120 mm OD slitting saw, 48 rpm and part time chips looked too small, although few times I managed to clog the tooth space - lack of flood cooling,  I was using brush and dripfeeding tapmatic alu-fluid. Slitting saw cuts nice when chips are healthy looking eagle nails and not fine sand. IMHO. most slitting saws are destroyed running too fast/feeding too little (overheating, cutting the chips over and over into fine dust) or over enegetic feed an lack of coolat which caused tooth spaces to fill and jams the saw. The coupling housing was that big that I had to reposition it halfway and I was having the slitting saw inside. Nevertheless the whole piece was within 0,5 mm from straight. Which was not really necessary, but nice to fit before skimming excessive out.

Parting off is pretty hard when machine limits are reached and we hobbyist tend to venture where no-one dared. Sometimes with mixed results which is reflected by multitude of opinions about it.

Pekka

[AdeV]

Personally, I'd go with the T-slot cutter, I find slitting saws are too prone to wobble on the holder (resulting in too big a cut), plus as you're cutting on a circular surface, keeping the slitting saw "just so" engaged would, I feel, test the patience of a saint. At least with a T-cutter you can run it at a normal speed, feed it full depth & then use your rotary table as the ongoing "feed".