m16 studding work instead of ballscrews ?

[irving2008]

but have just bought some M10 A2 Stainless (which works out at about £3.87 a metre)....which looks like it'll be much better. I intend turning the ends down to 8mm to fit the skate bearings I have supporting the rod (which in turn are held by SK16 mounts).

M10 A2 is good; the main issue with the smaller threads is the pitch, M10 is 1.5mm, which makes for slow traverses unless you gear up but then that adds cost/complexity. TR12x3 is £11.40/m (at Marchant Dice) and arguably the best mid-range compromise IMHO between cost and performance

[HankMcSpank]

M10 A2 is good; the main issue with the smaller threads is the pitch, M10 is 1.5mm, which makes for slow traverses unless you gear up but then that adds cost/complexity. TR12x3 is £11.40/m (at Marchant Dice) and arguably the best mid-range compromise IMHO between cost and performance

Yeah... M8/M10 can be a little slow...especially with underpowered motors that I previously had! But hey, this is just a hobby (not my day job thank heavens - my family would be perpetually like a nest of newborn starlings) & I justify it by saying "Hey, I can resolve down to 1.5mm/800 steps = 0.0001875mm (as if lol). Also, I'm typically making stuff that's about under 100mm x 50mm (so it's not as if I need to cover a lot of real estate fast!)

That's a good 'bang per buck' suggestion though - 3mm pitch is starting to get a little more like it ...but I guess then there might be a bit of a battle making your own delrin nuts? (then the cost starts taking off)

[Robin Hewitt]

M10 is 1.5mm, which makes for slow traverses unless you gear up but then that adds cost/complexity.

M10? I'd go for around M4 :whistling:

Okay you need to gear it up a tadge and hold it in tension but the frictional losses will be so much lower and no way could you pull M10 straight.

Real engineers from days gone by had no fear of disadvantaged gear systems.

You can't get 100% straight with anything but the thinner you go the better the approximation. There's a wonderful piece of accidental verse in the Oxford Dictionary or Quotations...

...and so no force however great
can stretch a cord, however fine
in to a horizontal line
that shall be absolutely straight

[BillTodd]

One point to watch out for is that the pitch tends to be slightly greater than standard on rolled threads (rather than averaging out), so a 100 turns on a 1.5mm pitch may well be greater than 150mm.

You'll need to calibrate the exact pitch when you set-up the axis params in mach or emc.

[edit] tip: if you are buying mail order, buy three or more lengths - they'll almost certainly be taped together when packaged so will be less prone to being bent in the post

[edit2] I don't see the point of using M10x1.5 over M8x1.25 - it'll have larger drag (because of radius & circumference) than M8 for little gain in pitch. Irving's suggestion of 12mm x 3 acme/trapezoidal from Marchant dice sounds a better option.

[edit3] As soon as I get my travelling steady finished, I intend making a 5/16" 11TPI with new roller nut idea, for my engraver .