My first cnc machine.

[seashaw]

Hi,

Yes the rail design will work fine but Personally I wouldn't use Ali angle has it wears quickly. I would just use Flat bar bolted to the front of Box section. Doing it this way will allow much more adjustment and make it much easier to setup.

Regards R&P then be aware that you probably need a ratio of 2:1 or 3:1 to get decent resolution. Direct drive with no ratio will have large pitch, You'll most likely use Mod 1.5 and even the smallest 12T pinion has quite large pitch, IE: Diametric pitch(DP) x pie so 12T = 18 x 3.141= 56.5mm Pitch.
Now because your not cutting and haven't got to over come cutting forces plus you can build a lighter gantry then you could probably get away with 12T but on the down side your Linear system won't be so efficient so more friction to overcome. So really larger pinion will be better for tooth engagement but this increases pitch, even 56.5mm pitch would be too much for me so I'd want 2:1 on that.
So going lager say to 17T which gives close to 1" DP which is more common pinion size used with R&P and would give 80mm pitch and this would require 3:1 giving nearly 27mm pitch. This is 3 x the pitch you'd have on CNC router and to me would be about right for plasma, thou I haven't much experience with plasma I do have friend who built one with direct drive and know it was no good and ended up have 2:1 ratio applied. This used Mod 1.0 thou which has smaller DP on same tooth pinions to MOD 1.5, thou I seem to remember him saying wished he's used larger Mod but can't remember is reasons.?

JazzCNC what a great reply!,

I see were your coming from with the wear of the angle, but ive ordered some.... getting to excited and jumping into things.

Its kinder going to be once its worn unbolt it replace with something better might even make a nice trailer ramp out of it.

I intend to use the mod 1 track with an suitable pinion, might be sounding dumb but what do I need to buy to make it run 3:1?

[JAZZCNC]

I see were your coming from with the wear of the angle, but ive ordered some.... getting to excited and jumping into things.

Its kinder going to be once its worn unbolt it replace with something better might even make a nice trailer ramp out of it.

Has usual with all things CNC it's not has simple just worn out rail. Stepper motors lose torque has the speed rises so any friction is to be avoided and has the rail wears the friction or sticktion will increase and you'll get stalling motors. Also Ali is soft and graby steel is much better.

I intend to use the mod 1 track with an suitable pinion, might be sounding dumb but what do I need to buy to make it run 3:1?

Timing belts and pulleys. I use HTD Series on routers/mills.

[seashaw]

Okay great. I intend to purchase my rack and pinion materials some time next week.
Having these materials will help me picture what I need to make regarding brackets for sticking it all together.

Started building my table today, A pic of were Im up to.


Its all braced up and tacked ready for welding.

Decided to do the table 2200x1200 giving me plenty of room inside for 2m x 1m sheets and gantry parking.

[Kerryfisher]

I used mod 1 rack on my machine, I was a bit unsure to start with thinking I might have been better with a size up, but it seems to be working a treat, I would use it again.

Some pics here of my setup https://plus.google.com/u/0/photos/1...75352601632753

Sean