Two years into working with the PRT... what to look for?

[jeffreymcgrew]

Hey everyone. Sorry to not be making it to Maker Faire this time in Austin!

So we've got a PRT96 with a 4G upgrade, and been working away for the last two years. It's not been in 24/7 use, but it has done it's fair share of work.

Everything is still working just fine. However, after two years, I'd like to know what to look for in regards to wear and tear.

We've kept it up, lubed the racks, all that sort of thing. And I've replaced the router bearings & brushes.

The only thing I can see so far is that our X-rails are getting a touch of a nub at the base of the "V" on them from wear, but it doesn't seem to be effecting anything yet. Our racks and pinions seem fine so far, but again I'd like to know what to look for.

Thanks!

[knight_toolworks]

pinion wear is one. I got about 400 hours out of mine and the pinions were getting a bit sloppy.

[Brady Watson]

Jeff,
You'll want to remove those areas of the X or Y rails that are getting ratty. A file, sandpaper or scotchpad will do the trick. They are the result of the carriage essentially forging the rails as it repeatedly goes over them, creating a little bit of 'squeeze out' of steel. If these burrs are left on the rails they will eventually contact the V-roller bearings and result in bumpy motion of the tool - and that will transfer to the cut. Regular maintenance with a brown scotchpad will keep them clean & smooth. I understand that this may be a bit un-nerving if this is the 1st time you have done it - no worries. Avoid using any type of power tool and only take off the jagged portions at the base of the ground rail. It is not uncommon to take off a tiny bit of blue powdercoating when doing this, so don't drive yourself nuts.

You definitely want to replace the pinions on the tool if you haven't done so already. It's tough to visually note wear. A good test is to check for motor vibration - as a result of cogging/worn pinions and clean/replace as necessary. The Z axis is most often neglected in 2 areas - The Z axis pinion is not as easy to access as X or Y axes, and it should be lubed and checked for wear. As time goes on, the T-rail to v-bearing surfaces get forged/matted down causing the side to side distance between the rail edges to decrease (EG -Let's say, 4" wide when new, 3.9375" when broken in) Those who are somewhat mechanically inclined beware - There is some rhyme and reason to adjusting the Z axis v-roller bearings to take up this slop BUT you must only adjust ONE side (left most top and bottom OR right most top & bottom) to properly set pinion lash AND take up the slop between the v-roller bearings. Z axis pinion to t-rail rack tension should be very light to avoid two issues: 1) premature wear of the Z axis pinion 2) Z-axis tower spread that results in accelerated wear of t-rail surfaces - so take care when adjusting. FYI - proper tension of the motor turnbuckle is important. Check motor mount to carriage connection & make sure that there isn't any axial/twist play in it. Tighten as necessary. The correct number of turns on the turnbuckle is 3.5 turns after it has just begun expanding the spring.

Aside from these points, the machine is pretty much maintenance free. The pinions are where the rubber meets the road on these machines. Proper lubrication and timely pinion replacement is paramount to keeping your machine running in tip-top shape.

-B

[jeffreymcgrew]

Awesome. I'll order a new set of pinions today. I'll touch up my rails too. Thanks for the tip on the rails, that's a big help.

So I should just plan on every year replacing pinions like we do router bearings / brushes?

I've been keeping the rails clean and not allowing sawdust to build up on them, and I keep the racks and pinions clean as I can. I also check the motor mounts and such and keep them in shape.

[Brady Watson]

Jeff,
While it depends on how many 'miles' you run the tool, as long as you keep the pinions wet with grease, they should last you anywhere from 6 months to a year. Your tool should have 25T pinions on the X&Y and 20T on the Z. PRTAlpha 1:1 (for others reading this thread) use 20T pinions to gain resolution on all axes. PRTAlpha with 7.2:1 motors and PRSAlpha tools use 30T pinions (unless you have a 1:1 on the Z, then it's 20T - PRSAlpha 7.2:1 may have 25T or 30T on the Z) The 30T pinions are not as prone to wear (when properly lubricated) as the 20T or 25T pinions since more teeth are engaged in the gear rack. So replacement on PRSAlpha 7.2:1 powered tools will be less frequent than a comparable PRT-S with 25T pinions, mile for mile.

-B