any problems mounting teeth on rack up?

[AustinT]

I have been thinking the last few days of an easy to build table. The rack for the rack and pinion however has to mounted right side up. The rack will be above the level of the torch by 1 foot. I could mount it on the bottom of the square tube but it will still be exposed to splatter.
Thanks

[Luslugger]

With the teeth up there will be no shedding of anything that gets on the rack.
Bob

[ger21]

I've never used a plasma, but have read that they are very messy, with gritty dust getting everywhere. Including the rack I'd assume.

[AustinT]

Thanks for your replies. Ill have to see what else I can come up with. I was going to use 4 V bearings for the X axis. The rails would be a foot above the the table and would be made out of 3 inch square tube. Angle iron would be welded to the side of the tube so that the 90 degree edge was pointed in towards the table. The gantry would use the v bearings horizontally and push into these angle irons. A larger bearing such as a size 3 or 4 would be used because the weight of the gantry would be an axial force on the bearings. The radial force would preload the bearings into the angle iron. Only 4 bearings would be used for the x axis. Because the angle iron is welded to the sides of the tube it leaves the top of the tube open. This would have worked out great for the rack and pinion. The rack would have been on the top of tube. an axle would connect both sides and would be supported by 2 pillow blocks. The pillow blocks would mount on their sides on the gantery so that moving them up or down would change the preload of the gear on the rack.

Thanks for all of your help what a great forum!
Dan

[Vaughan Sage]

If dust simply flying UP is going to be main problem, how about designing in a METAL film seal made from very thin spring steel like shim. The seal would be a full length taught flexible band(s), anchored at each end. 4 largish diameter rollers would direct the tape seal around any torch etc inside a housing box, The splatter would not directly hit your Vee rollers, rack etc. Rack teeth downwards is still to be avoided as muck just builds up & gets rolled in tight, I have that on a LaserKomb paper cutting from Germany... Old defunct waiting for me to try building a CNC drill/mill.????

[systemfoxtrott]

Originally Posted by Vaughan Sage If dust simply flying UP is going to be main problem, how about designing in a METAL film seal made from very thin spring steel like shim. The seal would be a full length taught flexible band(s), anchored at each end. 4 largish diameter rollers would direct the tape seal around any torch etc inside a housing box, The splatter would not directly hit your Vee rollers, rack etc. Rack teeth downwards is still to be avoided as muck just builds up & gets rolled in tight, I have that on a LaserKomb paper cutting from Germany... Old defunct waiting for me to try building a CNC drill/mill.????

I think you got it Vaughan teeth up no matter what and debreeis an issue.Im going to ponder over what your saying about this tape seal idea.sounds doable .We used a mesh that looked like what the midevil body suits were made of for debree but I can not remember the nameof it was but it worked.

[csrc]

Originally Posted by Vaughan Sage If dust simply flying UP is going to be main problem, how about designing in a METAL film seal made from very thin spring steel like shim. The seal would be a full length taught flexible band(s), anchored at each end. 4 largish diameter rollers would direct the tape seal around any torch etc inside a housing box, The splatter would not directly hit your Vee rollers, rack etc. Rack teeth downwards is still to be avoided as muck just builds up & gets rolled in tight, I have that on a LaserKomb paper cutting from Germany... Old defunct waiting for me to try building a CNC drill/mill.????

Sounds like maybe a wide tape measure spring might work, flying with the gantry.If you used a brush wiper and some WD40 the spatter would likely not adhere to the spring.

CSRC

[Bloy2004]

Although I haven't implemented it yet, a possibility would be to use an air jet mounted to travel along the gantry pointed at the rack to lead and clear the teeth as travel takes place. this could be controled from the software and only occur in selectable time intervals.
Besides.. the sound would be cool.....pshsst! pshssssst.!!

This is the machine I'd like to do this to...dropping the flexible air line from above: http://www.cnczone.com/forums/attach...chmentid=11096

..although the racks on this machine are on their sides....

[chineguy]

This would be prone to debris for sure. The cover idea is something similar to designs I have seen used on various machines over the years. Many used a fabric reinforced rubber though. They usually had a internal clock spring style roller to maintain the tension. It might be a time consuming pain to get one to work just right. That's not to say that it can't be done though. Keep in mind that any extra drag that is added will likely need to be compensated for in your drives.

[AustinT]

Ive decided to rethink my design . The previous design although really easy to build had raised rails and the rack facing up. From what I have read these could both be a pain to deal with

Thanks for all the posts