Breakaway torch carrier design

I'm designing a LinuxCNC 5'x5' plasma table and modeled up my torch carrier in Fusion.  The design has 8mm linear bearings to allow the torch mount to slide up and make contact on the roller limit switch for material sensing.   I've also designed in a magnetic breakaway for the torch holder.  Attached are 3D renders of the back plate, breakaway plate and the entire Z-axis assembly.  

The breakaway torch holder and the back plate will be indexed on .5" ball bearings mounted in the back plate as shown.  I've allowed for up to 4 pairs of opposing magnets (on both the back plate and breakaway).  If I find 4 pairs is too strong to allow the torch to breakaway appropriately, I can try 3 or even 2 pair.I have a plunger limit switch mounted through the breakaway plate and contacting on the back plate to signal when the torch breaks away and trigger an Estop.

All the assembly components will all be milled out of aluminum.  

In the 3D model you can see how it mounts on the Z-axis gantry which is an OpenBuilds C-beam 20x80 aluminum extrusion linear actuator.  That gantry plate on the actuator is only 3"x3" and is leadscrew driven.  The Z axis actuator is rated for 26 lbs force.  I'm hoping the weight of this assembly (which is a total of 10" long) doesn't put so much moment arm stress on that gantry plate in high acceleration movements.  Fingers crossed.

Please feel free to reply with any suggestions for improvement or any problems you see in this design.  

Cheers and thanks!
-Dave

 

 

No eBay APP ID and/or Cert ID defined in Kunena configurationYou might find three balls to be more stable (like the three-legged milking stool).
Also, possibly make the mating part as a groove, so that they can all settle in to a repeatable position (basically somewhat like a touch-probe)

For the carrier rail I have long thought that a (second hand) guided pneumatic cylinder might be a good starting point. Then you can regulate the spring rate (and even vary it during the phases of cutting). They also generally have limit-switch mounting built-in.

An example, just to indicate what I am talking about:

Thanks Andy. Those guided pneumatic cylinders look def look interesting. I've already got the parts for the linear bearing & rods. That idea would have saved me time on the mill tho. At 30-40 bucks I might just grab one of those to play with tho.

I'll give the 3 bearing idea some thought.

Not sure I follow on the groove suggestion though. Are you saying the balls should index into a groove rather than a dimple? My thinking on the ball & dimple is it indexes in all directions. Ball and groove would only index perpendicular to the groove and still freely move along the groove? Maybe I'm just being dense here and you mean something different.

If the three grooves are at 120 degrees to each other (actually, as long as they are at three different angles) then it is perfectly constrained, but not over-constrained.
The grooves do not need to be very long. Maybe only a couple of mm. Just enough so that there is enough wiggle-room for all 6 flat sides to touch their ball.

TBH for a plasma it probably isn't all that critical, but the touch-probe I just finished has a similar setup that settles to within 1 micron.

Ok yeah now I get it. That makes total sense. Duh! Probably a lot less sensitive to how well I press the balls into their undersized holes and/or machine the dimples to match. To not have any play that was going to need to be precise and I was a little worried about how that might go. It also explains your 3 ball vs 4 ball suggestion a great deal.

Thanks a bunch!

I have tried a few versions of breakaway torch systems, all without much success. 

The biggest issue I find is not locating the torch, rather getting it to stay put. I currently have 10 'strong' magnets (20x5mm) holding my torch on and it's not strong enough. 

Keen to see how you go with the magnets holding the torch on.