A QCTP question, or two

I have thought of making some extra holders for my Myford type QCTP but have been put off by the difficulty of machining the two V 's at the back of the holder so that they are a good fit in the toolpost.

I thought of mounting the blank at 45 degrees and using and end mill to cut the V slots at the same set up but was unsure if I could get the required accuracy this way.

Can anybody suggest any other machining set up for getting the V slots spot on?

Doug

Doug,

That's how I did mine. It worked quite well enough for the knurling tool that is illustrated above. I guess you could mount the blank vertically and use a 45 degree dovetail cutter. Someone will now shoot me down in flames for suggesting the use of a cutter this way and I haven't used one like this so it might work or not! Harold Hall describes cutting dovetails for his grinding rest using end mills with the workpiece at an angle. If that is good enough for him, it's good enough for me!

John

P.S. And I used a narrow woodruff cutter to make the tee slot-style register in the back.

I'd mount the block flat and cut the V's with a drill mill like this.

**LINK**

I bought one on eBay for about £20.

Available here as well if you can't find them on eBay.

http://www.shop-apt.co.uk/drill-mills-chamfer-cutters-2-flute-altin-coated-carbide-45hrc/drill-mill-12mm-diameter-90-point-12mm-shank-altin-coated-carbide.html

Edited By Vic on 25/12/2015 11:26:02

This thread has shed new light. I assumed the problem would be getting the two Vs exactly lined up and the clamp slot would be the trivial part.

For a non critical application the Vs could be made one sided, probably best just the outside faces. Also with home made ones where you know the tool to be fitted some more customisation would be possible with a narrower tool slot and more overall height to give the single sided V more contact length to reduce twisting error.

BTW the price if wedge type in the 'states has dropped to almost the same as piston type so that will, with usual markup, be over here in due course. There is a far eastern source of course if you accept that risk.

Doug and John,

Blocks set at 45 degrees for me as well, I set the angle roughly with a guide and then check using the DRO. You can set it very accurately, just need to calculate where the cuts should be to get the correct separation of the "Vs".

The chamfer ended cutters linked by Vic today (his first link) are the 30 degree version, and I think he might have meant a 45 degree version instead. They do exist (see his second link), but I wonder what is the difference in the resulting groove from a conventional end mill at 45 degrees?

After all this advice and the tales of assorted woe I think the only way to buy a QCTP set is to have the bits in your hand to try. Thanks everyone.

Cheers

Tim

Edited By Tim Stevens on 25/12/2015 14:33:14

Yes I meant 90° Tim, I looked at the picture and didn't read the description on the first link!

The second link is 90° but they do sell other angles if needed.

For DIY enthusiasts, this thread might be of interest.

MichaelG.

Lots of good advice about making the toolholders. 45 degrees and using an endmill for the V's would be the cheapest solution,and since it seems to work , I will try that. I have a DRO on the mill so that will help with the positioning of the V's. I like the fact that the bought ones are hardened but that would be a step too far for me.

Now where did I put that lump of 30mm steel plate that has been knocking about in my workshop for years.

Doug

Now that the drinking season is slowing down (a bit), I've had a chance to reflect on this question. Although it was a while ago, I now fecall that I used my 45 degree vee blocks to hold the toolholders on the mill table. If I remember correctly, it took a bit of fiddling about with clamps, angle plate, etc., but did it in the end. There's more than one way to skin a cat!

John

I've seen this on another forum. It's interesting that he had two goes at cutting the V's. The first roughing cut made with the holders clamped in the vice at 45° and then a finishing cut with them clamped flat but with the head of the mill canted at presumably 45°. I'm guessing it's easier and more accurate to machine the holders with them flat in the vice? I think it's the way I'd do it if I didn't have a drill mill.

I'm back with some more information which might be of interest.

Just managed to upload the 3 photos after 3 attempts...so here goes.

Clive Foster suggested that I use round bars to support the holders whilst measuring, I can report that all the measurements made on round bars were within a couple of thou of the first set, where I used ground square bars supported in matched v-blocks. (see earlier in the post)

This alternative set-up did allow me to check the location of the v's by measuring the width across the two bars (short lengths of 1/4 silver steel) and subtracting one diameter, the result (4 different makes of holders) was all within +0.03mm to +0.08mm of the 48.00mm stated specification for the T00 sized block.

I've just bought and modified a 1 inch linisher (from the big red and black tool-shed) to do the work (yes, the slot is 1 inch wide - how lucky is that) and so far have fettled the worst of my errent blocks so they now lock positively at <> 50% on the cam as per the original Bison blocks - result.

The linisher, as bought, needed a thinner belt platten to get the belt into the quite narrow groove, a guide/stop and suitable shims were required to set the cutting depth. A little piece cut-out of the side of the belt was needed to feed the block into position. The resultant simple grinding procedure was done from both sides to reduce any potential error. I know that the slots are not absolutely true, but the blocks were essentially scrap and now they clamp-up very well. Fitting a new abrasive belt, now that I have fixed the worst offender(s), should improve the precision of the slot as lighter cuts will suffice on the remaining holders.

My ruler just happened to be the correct thickness to set the depth of cut for this holder.

Based on potential savings over original Bison blocks, I'm quids in. Although I still wonder how manufacturers produce precision v groves to the tolerances shown above, but are unable to get the clamping slot anything like correct for a T00 QCTP, clone or otherwise. The worst case for me, needed the best part of 1 mm removed - the holder as delivered only just slid onto the block.

This is the holder that would only just slide into place - no locking action at all, now after grinding, a nice positive 50% lock position.

Michael G's remarks on what are acceptable quality levels rings true - here I am, happily sorting out a very obvious manufacturing error, the distributor being unaware unless they follow the forum.

When is a T00 QCTP not a T00 QCTP - when its a clone.

Phil

Edited By CotswoldsPhil on 28/12/2015 19:33:12

Well done Phil. Really glad you have a good result by decently simple means. I'd probably have splashed out on a good carbide centre cutting end mill, machined down the back face to get a flat flange at the right position then screwed'n glued gauge plate flats on to make a new Tee slot with the clamping surface in the right plane. Tapping might have been a bear if the material was the near tools feel used on industrial rated holders.

Round bars make it easy to check both the Vee spacing and parallelism of the Vee axes. Also work well to check that the clamping side of the T slot is parallel to the planes of the Vee. Would have put money on the error being due to planes of the Vees and T slot clamping plate being mutually out of parallel rather than the absolute dimension error you found. Out of parallel is the likely error if you get a bit careless with simple grinding set-ups. The dimensional error you found is basically not watching wheel wear so failing to make the necessary compensation. Which basically says the makers know that the production process is designed to produce out of specification parts and just don't care. A couple or three thou variation is plenty for finish grinding. 40 thou / 1 mm is beyond outrageous. Wonder how much error is on the Vees and how much on the T slot flange as wheel wear errors will be additive. In series production its always good if you can make tooling wear and other errors roughly opposite rather than additive so things tend to cancel out.

Clive

Morning Clive,

It did not occur to me to check the 48mm at each end of the block / v to check for parallelism. I've still got the set-up so will take a peek. All very interesting this - I'm not a toolmaker, this is just a hobby for me.

Regards

Phil

I made up a Dickson toolholder for my Bantam perhaps 18 months ago and used it as a DTI mount. It was as much to address the challenge of how to make it as address the need for one.

If (like me) you intend to achieve the required vee features by using a standard milling cutter (4-flute end mill in my case), you may as well also measure it up with the body at 45 degrees. Otherwise you are measuring the vee dimensions and then having to translate them 45 degrees to the coordinate system used by the cutting process, using the square root of 2 many times.

The vee features are clearly square (90 degrees) and are at 45 degrees to the front face. So, mounting the sample at 45 degrees, you can measure the (now horizontal) features and distances directly using a standard height gauge or in my case, using the DRO on the milling machine.

Its perverse to measure the feature coordinates at one orientation and then translate them to another surely. A 3-axis DRO with a resolution of 0.01mm or so is ideal for acquiring the dimensions and also for implementing them on the workpiece. Theres no point making work for yourself.

When I try to add an apostrophe, I end up with bizarre accents, graves etc. Some sort of Windows thing presumably.

Murray

Hi Muzzer,

I'm not intending to make any holders, my aim was to check the dimensions of the 11 commercial holders I have, 5 of which don't fit my tool-post at all because the clamping slot is too shallow. Checking the width of the V's was just a side-show and proved that any poor fit was not due to manufacturing errors in the V's.

The only metal I'm cutting is to increase the depth of the existing slot to make them usable i.e. able to clamp-up positively. With the set-up shown, I've been able to establish how much needs to be removed from each errant holder to get them to fit.

Regards

Phil

I don't want to labour the point, but, before you go about re-machining or re-grinding the vees, have a close look at the clamps. My original ones didn't do the deed properly out of the box. I ended up making new ones with a (VERY slightly - like gnat's kneecap) thicker width to the clamping bit. (I'm sorry, I can't think of a better way to describe it!) That did the trick. The thicker clamp pulled the tool holder closer to the vees, bearing in mind the rather limited movement provided by the eccentric pin.

John

Must make some Barry Jordan style carrousels to hold them sometime

Edited By KWIL on 24/12/2015 10:15:01

I am interested in the carousel toolholder, - anybody have any links / pics ?.

Cheers

Hi John,

I have no intention of touching the V's. The are nicely ground and accurate as far as I can measure. All my measurements have been to establish how much to remove from the working face of each clamping-t-slot (all 5 are different and too tight) to allow the clamp to operate in its correct position, which seems to be the opposite of your situation. The original Bison holders are a perfect fit, so redoing the clamp is a non-starter, I would then have 2 Bison holders that are too loose. My aim was to have all my clone holders clamp to the same position as the Bison's.

If you take a look at the linisher set-up (a couple of posts back) you will see the method I have used to relieve the slots. I set the measured discrepancy with a shim, in this case 0.0315 inch (the worst one) and conveniently the thickness of my ruler, between the fence I made and the holder when the working-face of the slot was just touching the belt. Everything was set-up square beforehand - table / platten / fence / belt tracking. I removed the shim and linished away, until it all sparked out, having turned the block over about a couple of times to even out any potential errors.

I've just completed the rest of the holders this afternoon (much less metal to remove) and all is now well in my workshop, having 11 usable holders, instead of a pile of scrap.

Phil

Phil,

Glad you got it all sorted. I obviously got the wrong end of the stick. Apologies. Happy to have solved my problem relatively easily, then.

All the best,

John