Substituting ACME with Trapezoidal ("Metric" ACME)

[rikun]

Hi,

I have a slight problem. Actually I'm not building a cnc machine, but a motorized film camera rig It's quite similar, but it only has two separate X axis'.

I already have a lead screw and bunch of stuff for it from dumpstercnc.com. It is Trapezoidal 12 mm x 1 start (the metric equivalent of 1/2" Acme).

I would really like to use Ahren's stuff, mainly the excellent bearing blocks, but they are 1/2" Acme. I was thinking if I could substitute the bearing with something that has the same OD, with the inner diameter of 12mm...? Actually the whole Z-axis looks like what I'd need... Except I have the dumpster nuts.

How about the low-profile blocks? Would it be possible to change the bushing myself? Do you think suitable bushings would exist (same outer diameter as the stock, but 12mm inner diameter)...

I really hate this imperial/metric stuff, makes my life so much harder. I'm already convinced that selling my metric aluminum extrusion and importing imperial from the States is the only way to get this done "easily"...

Getting bearing blocks made locally would cost me a lot... And basically there's nothing wrong with Ahren's design except I'm in metric land..

Any fresh ideas? My existing profile is 50x50 mm and has a spacing of 50 millimeters between t-slots (if getting wider profile).

[RICHARD ZASTROW]

rikun, just FYI, ACME threads have 29 deg. included thread angle while ISO Trapezoid have 30 deg. included thread angle. If you already knew that, never mind this. LOL

Dick Z

[rikun]

Yes I knew that.

If anyone knows where I could buy fractional extrusion in EU that would be good too.

But I think I'm going to go with metric and get my own custom bearing blocks made by local school. Now I'll just have to draw them, sigh...