PH Engineers: Screw thread expert required
Discussion
We have a small issue with some prototype products that we have whereby two parts screw together nicely but then wont unscrew. The male thread is visibly poor but our supplier is asking for an independent report - We've previously used "The Spring Association" in a similar situation we had with springs, but I don't think "The Thread Association" exists!
Does anyone know of somewhere that could do such a thing for us? It's an M55x1.5 thread
Does anyone know of somewhere that could do such a thing for us? It's an M55x1.5 thread
If it's been machined poorly then it could well be the burrs are hanging up on each other. Maybe due to a blunt tool in which case it's down to the manufacturer to correct the problem.
Does seem awfully fine thread for a 55mm OD though, I'd have thought 2-3mm pitch would have been a better idea but i couldn't say for sure without knowing what it's for..
Does seem awfully fine thread for a 55mm OD though, I'd have thought 2-3mm pitch would have been a better idea but i couldn't say for sure without knowing what it's for..
sultanbrown said:
He's right.You should simply have some "go - no go" gauges ground up. Keep some for yourself, and give some to your supplier.
Associations aside, that's the experts answer.
If you really want to go bezerk, then get the drawing office to produce some shadowgraph templates, and get a shadow machine.
http://en.wikipedia.org/wiki/Go-NoGo_gauge
http://www.baty.co.uk/product_selection_projector....
It's just basic engineering QA.
Edited by dilbert on Thursday 13th November 10:31
roboxm3 said:
blindswelledrat said:
I have no idea why I clicked on this thread or why I find it curiously fascinating.
Same here; I even tried to think about why the problem may be occuring and how it could be fixed.....like I'd have the first f
king idea!?!? 
How odd we all are
sultanbrown said:
When my customers had problems with parts from their other suppliers, they would just pop them over to me and ask me nicely to have a look.
Should be able to measure every aspect of the thread in less than 5mins.
Sultanbrown, ex-quality manager, looking for work.
Should be able to measure every aspect of the thread in less than 5mins.
Sultanbrown, ex-quality manager, looking for work.
Frankly I always find myself a bit spaced out by some of these threads. You have the government saying theres a skills shortage, and then all the people with the required skills are out of work.
By logic presumably that means all the people with no skills are in work, earning fortunes but paranoid about loosing their jobs!
Well done UK PLC.
Edited by dilbert on Thursday 13th November 10:54
dilbert said:
sultanbrown said:
When my customers had problems with parts from their other suppliers, they would just pop them over to me and ask me nicely to have a look.
Should be able to measure every aspect of the thread in less than 5mins.
Sultanbrown, ex-quality manager, looking for work.
Should be able to measure every aspect of the thread in less than 5mins.
Sultanbrown, ex-quality manager, looking for work.
Frankly I always find myself a bit spaced out by some of these threads. You have the government saying theres a skills shortage, and then all the people with the required skills are out of work.
By logic presumably that means all the people with no skills are in work, earning fortunes but paranoid about loosing their jobs!
Well done GB PLC.
We made a small stainless part and sold it for £3.50 each, at no profit (was part of a larger order of components).
The Chinese can supply the same part for 30p each.
That's pretty muched f
ked engineering in the UK.I've spoken to a thread gauge manufacturer but they say there is not enough thread on the male half of the product (5-6mm) to make a reliable go/no-go gauge.
Changing the pitch of the thread is, sadly, not an option as one of the parts is shared with other existing products.
I've also considered a shaddow graph but honestly it will be a wasted exersise in this instance - you can see how bad the thread for is just by taking close-up photographs
Dealing with the supplier is another issue that we dont really need to go into here, all we need is an "expert" to give us the evidence and their "expert" opinion.
The parts are made from a zinc alloy.
Whilst in use, both parts get to around 130 degrees.
Yes, it is a Chinese supplier
Changing the pitch of the thread is, sadly, not an option as one of the parts is shared with other existing products.
I've also considered a shaddow graph but honestly it will be a wasted exersise in this instance - you can see how bad the thread for is just by taking close-up photographs
Dealing with the supplier is another issue that we dont really need to go into here, all we need is an "expert" to give us the evidence and their "expert" opinion.
The parts are made from a zinc alloy.
Whilst in use, both parts get to around 130 degrees.
Yes, it is a Chinese supplier
Edited by Goochie on Thursday 13th November 10:57
Edited by Goochie on Thursday 13th November 10:57
I'd reckon these guys below should be able to help, or point you to someone who can prepare a proper report to show noncomformity in respectof major/minor diameters and thread profile.
http://www.midland-metrology.co.uk/
Or Sandwell weights and measures
There is a metrology lab on the Coventry University Technology park, don't have a link sorry.
From previous experience with this, you'll get the little buggers arguing till the cows come home unless you hit them with some facts. Unfortunately the volume of business may not support the cost of the objective investigation.
One day the collective brain dead unwashed in this country will wake up and realise that their (our) appetite for £4 kettles and £3.50 toasters has totally screwed over (pun- sorry) UK plc.
edited to sort link formatting
http://www.midland-metrology.co.uk/
Or Sandwell weights and measures
There is a metrology lab on the Coventry University Technology park, don't have a link sorry.
From previous experience with this, you'll get the little buggers arguing till the cows come home unless you hit them with some facts. Unfortunately the volume of business may not support the cost of the objective investigation.
One day the collective brain dead unwashed in this country will wake up and realise that their (our) appetite for £4 kettles and £3.50 toasters has totally screwed over (pun- sorry) UK plc.
edited to sort link formatting
Edited by F i F on Thursday 13th November 11:16
That is why it is important to get a report on thread form for both components.
As an aside some thread forms are deliberately designed to deform when you screw them in in order to achieve a good seal. A common example is the thread on the male part of a pressure gas cylinder like the oxygen bottle on a gas welding set. It's a one time use design. The thread on the valve deforms but the cylinder thread does not. Come bottle retest time the old valve is thrown away and a new one used.
M55 x 1.5 isn't such a thread btw. But if the two threads are from different suppliers you need to prove which one is at fault.
As an aside some thread forms are deliberately designed to deform when you screw them in in order to achieve a good seal. A common example is the thread on the male part of a pressure gas cylinder like the oxygen bottle on a gas welding set. It's a one time use design. The thread on the valve deforms but the cylinder thread does not. Come bottle retest time the old valve is thrown away and a new one used.
M55 x 1.5 isn't such a thread btw. But if the two threads are from different suppliers you need to prove which one is at fault.
Gassing Station | The Pie & Piston Archive | Top of Page | What's New | My Stuff