Lead size for metric bolts.

Hi folks...I'm as far from being an engineer as is possible - woodworkwe actually.

Due to lockdown and my health problems, I can't go out and find the answer to my question in person so I hope you'll forgive what might be a daft question:

Is there such a thing as a chart that shows the lead (travel) of M sized bolts?

I'm trying to build a woodworking jig using threaded rods. This would, by turning a threaded rod in a captive nut, enable me to move wood in regular increments along on either a table saw or router and cut the fingers of joints at adjustable but repeatable spaces.

Hopefully, by using (for example) an M10 threaded rod and turning it a number of complete rotations, I could measure cuts of 6mm, 8 mm etc.

Sorry for invading the metal with wood-related things.

Hi Mel. ..all the commonly available threaded rod and fasteners use Metric Coarse Pitch as the standard issue, unless stated to be otherwise;

Wikipedia ISO Metric Screw Thread

..M10 will give you 6mm in 4 turns, but getting a convenient number of turns-at-hand-wheel for 8mm spaces from the M8/10/12 coarse sizes might be a pain - if this is important, 1mm pitch Fine thread bar is available in larger diameters as illustrated here (although I'm sure other suppliers also stock it).

GWR Fasteners Metric Fine Threaded Bar

..depends on how much handle-turning you find acceptable!

Edited By DiogenesII on 19/05/2020 07:40:20

Edited By DiogenesII on 19/05/2020 07:41:44

As our Sinopean friend says, there are really only two standard (read: easy to obtain and cheap) options if you want an integer number of millemetres per revolution. These would be M6 x 1 or M16 x 2.

If you can live with turning partial revolutions and using a graduated dial on the end of the spinny bit, M10 has a lead of 1.5mm, so you need 2/3 of a turn for 1mm and 5 2/3 turns for 8mm.

Dividing the dial into three is easy with just a pair of compasses and straight edge (a method known at the time when Mr Diogenenes was most active).

You could also use M10 and gear it down by a 2:3 ratio (look on youtube for Matthias Wandel and woodgears.ca for how to make wooden gears) so one turn of the "2" gear will give an integer millimetre revolution of the rod attached to the "3" gear.

Engineering problems are engineering problems, no matter what the material is.

You can get M10 x 1mm pitch threaded rod at quite reasonable prices which would make for far easier use, typical seller

You would have to glue in the matching nuts as the typical pronged or screw in nuts used by woodworkers tend to only be available in metric coarse.

Edited By JasonB on 19/05/2020 08:10:38

If you are thinking about making a jig for finger jointing or box combing, I made one years ago from a drawing I saw in a Woodwork mag. I was quite easy to make, nothing fancy and I,m sure it can still be found in those books.

The whole thing was made from wood, no steel anywhere.

Same here larry, finger joint jig just needs a bit of something to fit into the kerf of the first cut unless you want to do irregular patterns.

Edited By JasonB on 19/05/2020 08:45:20

Mel Wilde:

Your jig is likely to have backlash in its movement; not a problem as long as you remember to approach each destination from the same direction ie "take up the backlash".

Apologies from a fellow woodworker if the point is already obvious to you.

Thanks for all the information and advice about this subject.

I am aware of the wooden peg "spacer" jigs and there's a couple available commercially. To answer the inferred question "why build one like this?" - firstly; I want variable but repeatable joints. Secondly; the satisfaction brought by the process of making things!

Best reason to make something, it also avoids cumulative errors.

M6 is probably more than strong enough for a jig like this if you also use a parallel bar of plain rod to make sure it doesn't bend.

Neil

Where possible, use the screwed rod in tension, so that it is pulled straight, rather than risk it bending under compression.

M6 will deliver quite a force. Think of the mechanical advantage provided by a fine thread with a long handle to rotate it.

Howard