10 10 300 D What is Dimension "M"

[TJS]

Newbie here. I would like to know what dimension M is on 10 10 300 D. I am a little confused I guess with the drawings as I have to flip back and forth to see what I need.
Thanks.
T.J.

[astrolavista]

I'm thinking it's the width if your rack..

[astrolavista]

http://www.mechmate.com/forums/showthread.php?t=271&page=2

See Post 21

[astrolavista]

sorry see post 41

[TJS]

So what you are all saying is that I would need to mock up the rack first before I can drill the holes in the main beam for the x-rail to bolt to. Also Gerald's idea is good about drilling the holes smaller in the rail and then transferring the location of the holes into the main beam but if you have a transfer punch set you can drill the rail holes to final size (3/8") and then when you get it lined up with the main beam use a transfer punch to transfer the location of the hole to the main beam, of course after you determine dimension "M".
T.J.

[J.R. Hatcher]

When drilling the rails just let the tip of the 3/8" bit drill into the beam a little, then finish drilling the beam with the correct bit :)

[Gerald D]

Dimension M is not the width of your rack. It is the space available for mounting the rack. (Rack widths vary from 3/8" to 17mm - depending on supplier/country)

Dimension M is affected by the straightness of the beams after welding and that is why it is not given as an absolute number. In theory, it is 21mm, which allows 4mm weld distortion for the guys with 17mm racks.

[TJS]

Dimension M is not the width of your rack. It is the space available for mounting the rack. (Rack widths vary from 3/8" to 17mm - depending on supplier/country)

Dimension M is affected by the straightness of the beams after welding and that is why it is not given as an absolute number. In theory, it is 21mm, which allows 4mm weld distortion for the guys with 17mm racks.

Gerald,
Thanks, but still a little confused so I drew a picture. The line in the red would represent a straight edge. So the "M" distance = Rack + Tape. Correct me if I am wrong.
Thanks.
T.J.
http://www.tjsperformance.com/images/Dimension%20M.bmp

[Gerald D]

Yes, the rack is mounted flush with the outside of the rail, to get the pinion gear as far onto the motor shaft as possible. You should have a generous gap between the rack and the channel (or tube of y-car).

That gap gets eaten up by crooked channels, or odd-sized racks, or odd-sized/shaped gantry tubes. Some folk have tried to reduce M, thinking they want less gap and less rail overhang. However, the laser cuttings dictate M for the gantry.

[Gerald D]

Do you realise that your sketch is nearly 600kB! You used .bmp format . . . . . . . here is that same sketch in .gif format, using 200x less memory at 2.6kB:

3805

[TJS]

Ya ya i know Gerald. I had it a .gif and it would not FTP up to my web hosting company. I was kind of in a rush too. That is why I did not attach it.
Thanks.
T.J.