What's the teminology?
|Simon Williams 3||22/07/2018 14:38:15|
|491 forum posts|
Hello all, cor ain't it 'ot!
I have recently found myself repairing an exhibition stand, where the flat panels have 16 mm rods each sides to hold them together. I discovered that the thread I thought was M8 in each rod was actually 8 mm OD, but was two start. So the thread pitch is actually 2.5 mm not 1.25 mm.
Which led me to wonder how such things are specified. The thread pitch measured with a thread gauge is 1.25 mm, but would I be right in supposing that, if I needed to specify such a thing to a professional turner I ought to call it "M8 x 2.5 pitch 2 start" (assumed symmetrical)?
Look forward to hearing what the forum thinks?
Thanks as always, Simon
|535 forum posts|
You are right, thread diameter x pitch (or lead) of thread and number of starts. I have used multi-start threads in designs over the years but most have been buttress or acme and in larger sizes.
938 forum posts
On my pen making have up to 5 starts, and that's just the way to specify it.
|Pete Rimmer||22/07/2018 20:27:55|
|679 forum posts|
You're nearly right. The pitch is still 1.25mm, but the LEAD is 2.5mm If you specify 'Thread 8mm, 2.5mm pitch, 2-start you'll' either get a 5mm lead thread or (more likely) an irate phonecall asking what it is you really want.
So ask for 'Thread, 8mm OD, 2.5mm lead, 2-start'
|535 forum posts|
Yes I agree with Pete, pitch is distance from one peak to the next, lead is distance travelled in one revolution.
Please login to post a reply.
Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!
You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.
Click THIS LINK for full contact details.
For subscription issues please see THIS LINK.