Damaged Screws & QCTP help!!!

Hello gentlemen

I find I am in need of your help again! I decided, on balance, to fit a quick change tool post to my chinese lathe. However, what started out as a good idea has lapsed into a nightmare!

I cannot budge the fitted standard tool post screw from the cross slide, so thought if I popped the cross slide out - I could access it from the back- but, thanks to rubbish Chinese hardware, the screws won’t come out and now the heads are stripped. So to Amazon to buy a damaged head screw remover kit. No problem. Annoying but it is chinese!

So I will need to replace these screws - but haven’t a clue what thread size to order! Please see attached photos. Any help or advice most gratefully received.

Thank you

Hi

threads per inch /mm pitch will help you.

How about checking the other treads on the machine to get a guess if they are metric? Or some other "Standard"

EDIT

how about hex socket head screws on the replacements?

George

Edited By george baker 1 on 29/07/2023 14:55:30

Hi George

All the bolts fitted to it that I have worked on are metric. The lathe is about 12 years old so presuming metric? I don't have any equipment to find out threads per inch or pitch unfortunately.

Margaret.

Use a ruler! Looks like there are about 6 thread pitches on the screw. Measure across the six pitches, metric and imperial. Dividing one my t'other, and inverting for imperial, will give an estimate of pitch (metric) or tpi (imperial) to 5% or so. Could be metric, imperial British or imperial US.

Looking at the height of the screw the pitch appears to be about 1mm aka ~25tpi. The diameter doesn't seem to agree with any particular thread standard, other than 7/32" BSW, which wouid be an unusual choice.

Andrew

Edited By Frances IoM on 29/07/2023 15:26:00

Bit undersize but Could be 6mmX 1mm. Try an ordinary m6 bolt in the thread and see if it fits. Order the right thread but in countersunk socket head HT and use an allen key..As to getting the old ones out, use a 1/4" wide cold chisel on the head to turn them.Tap them round with a hammer. Noel.

If it's not made in the UK or US, it's metric (99% sure).

I'd say 10:1 it's metric

Margaret

The usual form of damage head screw remover devices aren't terribly effective on this sort of screw. The head is too soft for the grooved wotsit to get a grip. It generally just cuts out a cone.

The only sort of extractor for machine screws and bolts that I've found to be anything approaching universally reliable are the grooved pin and hex turning device type sold by Rigid, Snap-On et al at seriously high prices. Drill the bolt, drive the pin in and around 90% of the time it comes out. Hafta accept that sometimes things will be immobile. Way, way too speedy for one job but I've had my moneys worth over a quarter of a century!

The tapered thread easi-out variety can work but are very hard and notorious for snapping off if you apply too much torque or are bit off-line with the spanner. Once snapped you have a really hard bit left stuck in the screw making the problem much worse as it can't be drilled out with normal tooling.

These days I just use a drill to take the head off in that sort of situation. I reckon your screws are M6 so 7 mm drill would do the job. With the heads off things can be separated and the sticking out stubs of the screws turned using a decent set of pliers. On relatively new stuff the threads are rarely jammed so the remains come out quite easily. Problem is usually due to the softish head being deformed when the screw is driven home by powered driver jamming it into the countersink. Slack fitting screws can cock over a bit inn then threads considerably increasing the amount of head jamming.

I recommend Maun parallel grip one for this sort of thing as the jaws are very well made and the parallel motion seems to give abetter hold than the usual pivot style. Spendy (£30 ish for the 160 mm flat nose ones I have) but good.

Clive

Edited By Clive Foster on 29/07/2023 15:37:39

Edited By Clive Foster on 29/07/2023 15:38:11

I'd also say metric, but the 5.69mm diameter is worrying.

A photograph blown up on a printer is a good way to measure pitch/tpi. Comparison of the diameter, to the length of several threads can usually provide a good estimate.

Thread gauges are an item that comes in useful fairly regularly? They do, for me.

Hi

there exists pliers for undoing screws by gripping them along their length. I gave a couple of pairs as presents a few years ago.

I suspect metric, but if people go to the "bolts on cars" thread you will find mixed thread standards are more common than we wish to believe.

George

Hi, I'd give the heads a few moderate taps with a pin punch and hammer or just use a piece of mild steel rod, slightly smaller than the heads, and then give them another try. The most important thing about cross heads screws, is to use the correct fitting driver for them, as there are quite few different styles these days, which don't have the same angles on them. It's not only Chinese cross head screws that get messed up this way, as plenty of British ones also do, especially if the correct driver is not used. Drilling the heads off would be my next thing to do, but you may end up with barely any of the thread protruding to get hold of, judging on how short those screws are.

Regards Nick.

Edited By Nicholas Farr on 29/07/2023 16:04:45

See if you can borrow an impact driver. Not worth buying one. Someone who plays with old motorbikes might have one.

Cheap will be cheap.

9 times out of 10 you can eyeball metric vs imperial, both UN and Witworth use a coarser pitch for a given diameter.

Edited By Fulmen on 29/07/2023 16:14:33

STOP RIGHT THERE Margret. You don't need to be undoing those screws to get to the toolpost stud so don't worry about getting the stuck one out and put the other back.

You need to wind the moving part of the top slide off the base and then you should be able to dribe the stud down & out

My bet is they are poor quality M6 x 1 x 10mm long

Edited By JasonB on 29/07/2023 16:38:25

Thanks everyone. Things are not going well!!!

Jason B - in my eagerness to get this sorted out - I took the advice given and used an impact driver. Just a gentle tap and both heads of the stuck screws sheared off! Your post hadn't come in about not having to remove this part - and now I am in a mess - big time!

I can't get the round scale part off to even attempt to get to the now broken screws - the circular part won't wind off - is it that little pin device stopping it? How do I get that out?

Also, I cannot budget that big stud. I have tried the two nut method, nothing. It seems to be threaded into the cross slide - is that correct? - it just will not budge.

Oh dear - I am so stuck! Help!

SOUNDS as though loctite has been used. Some heat will cause expansion and the loctite will give up. Do you have a small blow torch ? As Jason says it should be able to drive it out - put the nuts on the top to protect the thread. Noel.

Hi Noel, thanks for the reply. I took your advice and added a little heat and gave it a small tap and it popped out. Yey!

But now I find the two posts are different! The one in the kit is threaded both ends - have I purchased the wrong kit from arceuro? The one on my lathe is a push in fit, the kit one threaded. (My lathe is an Amadeal CJ0623b if that helps?). The videos I watched on ebay it was a straight swap!

Also, I have identified the little pin which seems to be stopping the circular part from moving. How can I remove this please?

I am at my wits end! I wish I hadn't bothered and stuck with the 4-way tool post.

Thanks all

Margaret

Some but not all roll pins on teh far eastern machines have an internal thread so you can put a screw in and then pull on the screw but not sure if your one will.

Not sure it screws together anyway