Metric Fine Grub Screws

[Malcolm TimmisParticipant @malcolmtimmis62417]

Nearly in the finishing straight to complete my first build, an oscillating engine to plans from 'Pete's Engines', (fascinated by the video's). Drilled and tapped M3 to lock the eccentric to the crankshaft only to find the M3 grub screw to tight. Why?, because the taps I have to hand are fine thread taps and the grub screws are Course thread, of course!. So, three hours on web-sites found no one who could supply Metric Fine thread Grub Screws.

I have no wish to declare my Fine Thread Taps redundant before they have some use, so, can anyone, please, tell me where I can find M2,M3, M4,M5. Fine thread grub screws so I can finish my engine for Xmas, (now three years in the build).

Heart felt Thanks to anyone who can help.

Mac

[Malcolm TimmisParticipant @malcolmtimmis62417]

Fine Thread

[Clive Brown 1Participant @clivebrown1]

I think you'regoing to have problems wth this search. Metric fine are always going to be rare for model engineering. I'd bite the bullet and buy the metric coarse screwing tackle for general use.

Sorry for being a pessimist!

[Tony Pratt 1Participant @tonypratt1]

Don't think I have seen metric fine grub screws in a lifetime of Toolmaking.

Tony

[old martParticipant @oldmart]

You might find some fine threaded screws to make into grub screws with a screwdriver slot cut in with a junior hacksaw, just like they used to be in the old days.

[DC31kParticipant @dc31k]

Where did you manage to find a tap set with M2 through M5 fine pitch?

Have you measured the pitch of the tap? M3 fine seems to be 0.35mm pitch.

Have you measured the pitch and diameter of the grubscrew to confirm it is M3 x 0.5?

M3 x 0.35 male threaded anything at all seems not to exist (smallest metric fine I could find was M5).

Even the next size up, M3.5, does not seem to be available as a grubscrew, but you could make your own from a standard fastener (e.g. modelfixings have them).

Possibly go to #6 UNC or UNF as grub screws in these threads are available.

[JasonBModerator @jasonb]

I've seen them in M6 x 0.75 from Modelfixings but nothing smaller.

I'd also be worried about stripping a fine thread with the grubscrew as you tend to tighten them quite hard to stop things slipping.

[D.A.GodleyParticipant @d-a-godley]

As a customer , I have always found “Spalding Fasteners ltd “, very helpful, they carry a good range of product , but perhaps not metric fine .

At the very least , a chat with them might help , even if only to point you in the right direction .

I have absolutely no connection with them ,other than an occasional buyer of fasteners .

[Speedy Builder5Participant @speedybuilder5]

Don't even ask the price !!!

MetricFine

[DC31kParticipant @dc31k]

Posted by Speedy Builder5 on 16/12/2020 20:37:04:

Don't even ask the price !!!

MetricFine

Interesting page. Perhaps you might be so good as to indicate exactly where on that site you found M3 fine pitch items. Thanks.

[Grindstone CowboyParticipant @grindstonecowboy]

M3 x 0.5 appear on this page, if it helps. They will send five as a free sample, it seems…

Rob

[DC31kParticipant @dc31k]

Posted by Grindstone Cowboy on 16/12/2020 21:39:54:

M3 x 0.5 appear on this page, if it helps. They will send five as a free sample, it seems…

That is good to know, but how does a link to a standard ISO metric coarse item help him in his quest for a metric fine item, the title of the thread?

[Speedy Builder5Participant @speedybuilder5]

Have a look at Custom-Order set screws on that linked page – That's why I said ….. ask for the price.

[Speedy Builder5Participant @speedybuilder5]

I am guessing that optical instrument trade may use fine threads.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Grindstone Cowboy on 16/12/2020 21:39:54:

M3 x 0.5 appear on this page […]

.

but not M3 x 0.35

Here’s a useful table: **LINK**

https://www.newmantools.com/tech/threadmf.htm

Sorry … I have no idea where to buy a few locally

MichaelG.

[JasonBModerator @jasonb]

As it's just the one that is needed you may as well "custom" make it yourself. Assuming you have the matching fine dies or can screwcut then thread a bit of steel rod and saw a screwdriver slot in the end. If you don't have the dies then redrill 2.5mm in another position and buy a M3 x 0.5 tap. and use an off the shelf metric coarse grub screw

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Malcolm Timmis on 16/12/2020 15:20:52:

Nearly in the finishing straight to complete my first build, an oscillating engine to plans from 'Pete's Engines', (fascinated by the video's). Drilled and tapped M3 to lock the eccentric to the crankshaft […]

.

Have you considered using an appropriate grade of Loctite [or similar) retainer instead ?

… or does the Eccentric need to be removable ?

MichaelG.

[Author]

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