M4 thread

[Ian GardnerParticipant @iangardner62867]

Hi,

I want to tap an M4 thread in the hub of a pulley I shall be turning, to fit the thread of an existing shaft. Can anybody confirm that it is 4 x 0.7 that is commonly used for prop shafts ie M4 course, rather than the fine thread, before I go spending money on the wrong size tap? I read that the course thread is the default (Wikipedia!).

Thanks….Ian

[Ian GardnerParticipant @iangardner62867]

Which thread- fine or course?

[Dave MilbournParticipant @davemilbourn48782]

Why not give MMB a ring? They make shafts, after all.

Dave M

[Bob Abell 2Participant @bobabell2]

Hello Ian

I've always used….M4 x 0.7 pitch

Tap drill….0.128"…..or 3.3mm………No30 drill

Clearance drill…….4.5 mm

Don't know the fine pitch info

You could measure your existing screw thread…..For peace of mind?

Bob

[Ian GardnerParticipant @iangardner62867]

Thanks both- I did consider ringing either Model Boat Bits, where I have bought shafts, or MMB but it seems just a bit cheeky- and this is presumably the sort of thing these forums are for!

I'm pretty sure it is M4 x 0.7 but just need confirmation before flashing the cash.

Bob- do you mean just measuring with a ruler or vernier, ie 0.7 between peaks and would that be accurate enough? I will try it though, with my newly bought digital vernier, just to see- thanks. As you can tell, not that experienced with things engineering but want to give this a go.

Ian

[Tony HadleyParticipant @tonyhadley]

Hope this helps,

Tony.

[Ian GardnerParticipant @iangardner62867]

Bob-just had a go and it does look like 0 .7mm- I think the fine thread is 0.5mm pitch. Should have tried that in the first place! I'll go for it.

Thanks again.

 

Ian

Edited By Ian Gardner on 20/05/2013 10:03:14

[Ian GardnerParticipant @iangardner62867]

Thank you Tony! That's got to be it. I was sailing Silver Mist on Sunday- my favourite at the moment-except for the noise of the gearbox, so I determined there and then to change the reduction to pulleys and an O ring, which should be quieter.

Tony, our last posts crossed I think.

Thanks all, for the help

 

Edited By Ian Gardner on 20/05/2013 11:32:38

[David Marks 2Participant @davidmarks2]

The convention used on Engineeering Drawings for metric threads is where the standard (coarse) thread is required, just the nominal size is defined e.g. M10 (which has a pitch of 1.5 mm). Where a finer thread is required, then the nominal size + the pitch are defined e.g. M10 X 1.25. For any metric thread, (due to a fluke of geometry) the diameter of the tapping can be calculated by subtracting the pitch from the nominal diameter e.g. for a M10 X 1.25 thread, the tapping drill required is 8.75 mm.

[Ian GardnerParticipant @iangardner62867]

Thank you David, for that useful information, which supports the idea that the course thread is the default.

Interesting about the tapping drill size too- I knew folk on here would come up trumps- always worth asking!

Ian

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