beginner problem with qctp

i’m a raw beginner, getting my head around machining with a Myford S7. I was attracted to getting a quick change tool post to help me get the tool height right - the lathe came with an “elephants foot” that needed shim etc each time I changed tools. I bought (perhaps wrongly) a qctp made by RDG tools. It works fine, apart from in one respect. When I drop a tool holder in, and get the height set as it should be, I then tighten the holder, but in doing so the tool holder sort of wiggles and the height of the tool changes by , I would say, at least a mm or two upwards. So I have to “aim off” and set it low. It’s a bit frustrating and makes the process more complicated. i would have thought that when the tool holder is slid in, it shouldn't make any difference when it is “locked”. It happens on all the tool holders, not just one. Is this normal? Do I have to live with it? Have I bought a duff tool post? Advice gratefully received.

Yes it’s normal, adjust then tighten check centre height of the tool if wrong repeat until right. You will soon get the hang of it. Once the tool holder is set for that tool it stays that way. Don’t forget to lock the adjuster.

That’s good to know! Thanks OS.

Roger, Oliver is correct, everything is perfectly okay with your holders.

To get a tool on centre height set it to roughly where you think it should be then use the point of the tool to gently nip a six inch rule against the diameter of the workpiece. If it's dead on centre height then the rule will be vertical - if pointing towards you it's too low, away from you is too high. Readjust the height setting screw to bring it vertical or very slightly towards you.

A tool will cut if very slightly under the centre but will dig in/rub if above

Hope that helps some more, good luck with your journey with your Super 7 I remember only too well my first steps- now they are coming to an end.

Tug

Edited By Ramon Wilson on 03/02/2022 13:24:29

Thank you Tug!

My 2d:

When I first read your query, it sounded to me as if you are just relying on the qctp locking mechanism to hold the toolholder in place. I may be doing you a disservice, but are you setting the tool on centre then bringing the [probably knurled] adjuster and associated lock nut down on top of the toolpost to hold the tool in position?

Sorry if your Granny already knows how to suck eggs!

John

No worries John . :- ) Sorry if my question was ambiguous! No I’m putting the tool in the tool holder and tightening the four bolts. Then I’m dropping the tool holder into position on the tool post. I then use the knurled adjuster to adjust the height of the tool against the work piece. I then “lock” the toolholder in place on the tool post and at that point the toolholder wiggles and the tool shifts up in terms of its position relative to the centre of the workpiece.If I do things is a different order and “lock” the tool holder then try to adjust the tool in it, it’s too stiff, and tricky to adjust. Have been doing it wrong and perhaps I should persevere with the second method? I’ll nip out to the workshop right now and double check. thanks!

Roger, you are not far off but you can't adjust the height of the tool with the toolholder locked into place.

The adjusting screw is just to determine the height of the holder. Set the tool - lock it - try for centre height - adjust if necessary - lock the adjusting screw. Job done

Once you are happy it's on centre line that's it until you regrind (if HSS) or change the tool bit.

I have a small digital height gauge that I use to set tool height, which reads in metric or imperial. I aim to get the tool to exactly an indicated 3.5" above the bed using this. To make a small adjustment, to for example raise the tool slightly, I release the locknut on the height adjuster while the mail holder lock is on, then tighten the adjusting screw downwards and just release and re-lock the lever. This gives a thou or two lift of the edge. To lower it, slightly slacken the adjuster, tighten the locknut, release and re-lock the lever.

Rather than having a setting gauge I measure the edge height as you can never be quite sure that the tool is lifting the setter up slightly.

I usually start with things a bit low and just nip up the locking cam, you can then screw in the adjuster and it will gently raise the tool upto the desired height then fully tighten the cam

If you leave the cam too loose then the whole holder sags down and you get the problems you describe

As Tug suggests trapping a 6" rule between the work and the tool will confirm centre height.
I use the same method but use a strip of plastic cut from a credit card in place of the rule, it's too easy to chip the inserts intended for non ferrous materials.

Emgee

I've not had good results with the 6" steel rule trick. Definitely make a center height gauge for more accurate and quicker adjustments.

thank you all. Your time and thoughts much appreciated. I clearly need to take a little more care and make adjustments bearing in mind the “delta” introduced by the locking cam. I’ll get there. I much appreciate the avuncular and friendly advice from you all to this newbie. I hope one day I can return the favour to newbies in the future.

Roger

The trick to minimising the locking cam effects is to snug things up a touch so the holder doesn't rock as you adjust the tool position upwards using the screw. The smoothness or otherwise of movement when doing this is a good test for the quality of manufacture of the set. Piston types are generally easiest to get smooth with a sensible drag but they also tend to be a little less secure. But cheaper. Wedge locking types tend to be most fussy about setting to get the right drag but they are more secure than the piston ones.

Dickson styles have a nasty habit of self adjusting when the locking device is turned if you don't snug the adjuster up properly. Dickson styles are also major league fine swarf magnets. Any locking issues developing in use are almost invariably due to fine swarf building up inside. But dis-assembly to clean out is a total doddle.

I've not seriously used Multifix styles so can't advise on those.

There is a reason why professional standard QC systems are so expensive. It takes serious precision to bridge the gap between "right every time, 24/7 and still working OK when the lathe is worn out" which is what the professional needs and "works fine but need to be aware of its little foibles" which is just fine for folk like us. At 10 to 20 % of the professional price a foible or two is fine by me.

There are numerous types of tool height gauge.

I'm a fan of the simple optical type.

Basically a transparent plastic blade 1/4" - 6 mm or more thick sat vertically on a base small enough to sit easily on the machine and heavy enough to be stable. Use a sharp fixed centre in the lathe headstock to scribe a line at centre height on both sides of the blade. Looking through the blade the tool tip is on centre height if both lines merge into one and are aligned with the tip. Or you can just use one line when working from the tool side.

I have two sets of lines on mine. One for the base sat on the bed and one for it sat on the cross slide. I also have a mirror attachment os I can set things remotely by looking down onto the mirror to see the lines and tool tip. My blade is only 1/4" thick. A thicker one 3/8" or 10 mm would be more sensitive to errors if not looking dead level to merge both lines. Re-making mine has been on the list for over 20 years now!

Clive

Thank you Clive for that detailed and considered answer. Much appreciated.

When I first used a lathe in an industrial environment it had a 4 way turret, and a box full of bits of packing, none of them thinner than a hacksaw blade. It was explained to me that exact centre height becomes more important as the work gets smaller, if you're say 1/64" wrong with a 2" diameter bar the front clearance and back rake will be wrong by less than 1 degree, which doesn't matter. If the work is 1/4" diameter you're wrong by 7 degrees which does matter. We didn't do much at that sort of diameter! I don't possess a height gauge, although I keep on meaning to make one. What I do is adjust by eye, then take a facing cut across the end of a bit of bar and judge how far up/down to adjust the tool by the size of the pip left. Obviously easier if your first guess was low.

4 tool turrets are horrible things, as well as having to mess about with shims I always kept catching my hands on the tool sticking out towards me

I have the same type of QCTP (RDG) and had similar issues at first. As described in several of the replies so far, it's just a matter of 'feel'. just drop them in and check the CH. I use a similar optical gauge to Clive Foster (simple & works well) clamp up and if not on CH just loosen with the lock lever a touch and adjust height with the knurled nut, lock again and 99% of the time you will remain spot on. If so, lock the adjuster with the cap screw.

One funny thing to watch out for (don't know if this is the case with all types of QCTP or just this make) - if you try to turn any hex material, be careful as even though tight to begin with, the vibration (even taking just a sensible light cut) loosens the whole thing - I had one or two disasters until the penny dropped. Just keep checking & re-tightening periodically as required.

regards Mike

Edited By Mike Hurley on 03/02/2022 19:51:37

All good advice, thank you. reassuring to hear people have encountered the same thing.