I'm no expert on this but we are using the 24T on a 4:1 so I would guess the 20T would be better, but I remember somewhere the guys talking about having to small a pinion doesn't give enough teeth meshing in the rack. Any comments people?

I use 24 T on my 4:1 as well. ( or was it 25 teeth :confused: )

Two problems with the 20 tooth: the smaller the pinion means less smooth running on the rack, more wear, and I think in a 20 tooth there's also (almost) no room for the axle. It's up to you but if I remember correctly you definitively do not want to go under 20 t pinions. I think with a three to one I would settle in between somewhere 21/22 T ?

I am in the (sane) metric part of the world, this matters when talking about pinions and mod !

Mine is 20PA with 30 teeth. I don't know what that translates to in metric module.

My reductions are 7.2:1 and 4:1 and they both have the same rack type and pinion.

I'm currently operating 3.6:1 (20t and 72t belt gears) with a 30t pinion (like Pete). I was using 24t pinion direct to start with (and used to cut out my belt reduction plates:)). On my last post (519) I was referring to the belt gearing not pinion gear to clear confusion, if any.

Hmmm, thanks guys. What I might do is try out my 30T pinions with 3:1 and see how it cuts. They are already at 1/2" so I'll just grab some 1/2" rod from TEA and run with that. If it goes pear shaped I'll shell out for different pinions.

Sounds like a plan to me, spend nothing first and if it works great you have saved more beer money. That's why I'm still using our 24T.

So now I am fighting to keep my surfaced spoilboard flat. Because of the fluctuating weather here in Sydney's west, from sub 20 C at night, sometimes mid 20 C during the day along with a few high 30 C days thrown in for good measure, my MDF top is changing shape. I have already surfaced it twice and now because of hot weather a few days ago I need to do it again.

Does anyone seal their surfaced MDF tops (if so what with?) or does anyone have any suggestions how I might keep the damn thing flat once I surface again this weekend....

MDF is like a sponge with moisture. But so are most woods. No different than not sealing a maple countertop on the bottom and watching it bow as the seasons change. Even steel moves with temperature. My MM is in a constant temperature and humidity room and the MDF changes thickness. Finding a suitable material that is impervious to temperature and humidity is near impossible but controlling factors is usually the route most try to go. If that is not feasible, you may be able to try to using an engineered wood that is made for weather like Advantech but be careful on your choices because like MDF the dust and chemicals may not be the best for the body. You can try sealing with a sealer but remember to be vigilant as a cut that removes the sealer will give an entry point for water infiltration. Sorry if this does not answer your question.

Bruce,

Pete is right.

MDF is good because it is cheap. But it is also wood so it does move with changes in humidity and temperature. Such is life with any wood.

A few of things to try (singly or in combination):

1) Thicker spoilboard.

2) Put down a 'better' sub-spoilboard, like thick (1" or 25MM or so) plywood, then glue thick MDF to it.

3) On the bottom side, I would consider putting a torsion box below the spoil board if it is extreme warping.

4) Worst case, go to a plastic spoilboard, like a big piece of HDPE (High Density Poly Ethylene). Probably still needs that on top of a more stable backing material or torsion box.

On the downside: Many of these will reduce your effective Z travel. Don't know how important that is to you in your situation.

5) One last thing... Box in the room with the MM, and run a small HVAC/heat pump that can also act as a dehumidifier. Keeping the temp and humidity in control should help. Also keep your stock in there for a couple of days before using it to acclimate it before cutting.

Just some thoughts.

Thanks guys... it is not so much warping, I have 2 layers of 18mm MDF with the top sheet of 18mm glued to the bolted spoilboard. All of these have been sealed with paint on every face except the surfaced bit. The movement isn't that much but is detectable in profile cuts, I zero to the table top and 90% of my cuts are perfect and do not touch the spoilboard itself, the other 10% will leave an onion skin of varying thicknesses. When I work immediately after surfacing I get 100% cut through without touching the spoilboard.

I guess when I get my dust collection worked out (yes, I have surfaced twice without it!) I can do a quick skim of the top if the weather has been nasty. My last efforts at 750ipm didn't take long....

Rightio, next question...

I designed my machine to take 2400x1200 sheets making sure I allowed the standard 50mm around all edges of the sheet. Well, for some reason it hasn't turned out like that. I have between 75 and 100mm at the 0,0 end and *just* miss down the 2400 end. The 1200 bit is fine. I checked all the physical measurements against my drawings and am pretty much spot on. However....

My question is.... which holes in the Y do you guys have your Z spider attached to? I have mine in the 2nd back from the motor side which allows me to use the big hole in the top of the Y to attach my cable chain for the Z. I have seen some using the 2nd back, some the 3rd back. My Z is standard aside from using a 2.2Kw spindle that sits on a 6mm adaptor plate.

Interested to hear your experiences in attaining the full 2500mm travel of the bit....

Just another note on the spoil boards, we have a 25mm MDF board bolt to the MM which we surfaced then coated in flooring polyurethane. I then attach a 16-18mm spoil board which I usually get a cover sheet from my supplier. Best sheets I have found are the moisture resistant ones with melamine coating. Just flipped the sheet over and did some pocket cuts with a .2mm depth variance.

Bruce, my spider is mounted in the furthest set of slots back.

Strange problem (when will they ever end!)

First though, I have been making my dust collection bits and making some changes.. My Z is now is the 3rd hole back from the motor side and all is now well with the spacing over the ends of the spoilboard. One good thing. My dust shoe is complete and is based on one of the commercial ones utilising magnets to hold the brush on.

However I have his ongoing problem with my Z motor. It couldn't pull the skin off a rice pudding and it gets far hotter than any other during cut operations which, in my option is strange.

It is strange because *all* my motors are the same, these: http://ausxmods.com.au/index.php?mai...products_id=13, all the controllers are the same (AM882's) with all the same settings. The pinions are the same (30T) as are the racks, all run direct drive (at this stage). All the motors are wired Bipolar Parallel and run at 50V. However, while I can't stop the X or the Y by pushing against them, the Z will stall at the drop of a hat, further amplified by the addition of the dust shoe meaning it will not plunge with the brush on at all (once the brush hits the job surface). There is absolutely no chance of ever lifting the Y or X off the rails by plunging the Z into the table. The gas strut on the Z just holds it one place and with the motor disconnected from the rack I can push it down and pull it back up again easily.

Now, I have swapped controller, swapped motors and pulled my hair out all to no avail so I am turning to you guys. Any ideas on this one?

You ran out of hair to pull yet? LOL

1) Gas spring too strong.
2) to much load on the Z-axis motor, i.e. too heavy
3) 24T worked for me, not 30T. 24 T has higher mechanical ratio.
4) add Z-axis 3:1 belt reduction will cure all

Z move the least, I assume you set full-current at rest like most did. pulls full current at rest hence the heat. if it moves more often, its cooler.

# I'd swapped to ball screw Z-axis after solving similar problem you encountered.

Just got back from the garage after trying something with no difference, I swapped the controllers between the Y and the Z. One thing I did notice that even after the machine had been sitting doing nothing for the past 4 hours the Z motor was too hot to hold my hand on it for any length of time, the X & Y motors were stone cold.

Tomorrow I will swap the Z and Y motors over to see what happens.

You should check the motor coils for continuity with a DMM before you swap them around.

Ken, just saw your reply.

1. Explained above, Z gas spring is easy to push up and down by hand and just (and only just) holds the Z in place. Replaced a stronger spring with this one due to being charged to high.

2. Could have something there although I have nothing but what usually goes on the Z (aside maybe from a 2.2Kw water cooled spindle) on the Z

3. Will spend some more money when I have it on lesser count pinions or will get my A into G and make my belt drives. However, don't want to attempt cutting aluminium with a piss weak Z.

All controllers are set the same, half current on idle, which is why I find the Z motor being hot while the others are stone cold strange.

# Would dearly love a ballscrew Z along with linear rails. Have both of those planned in the future

Thanks for your input, appreciated.

Cheers

Good point, will do.

I found the wiring for these motors to be strange, in biploar parallel mode the shafts spin freely and only lock up when power is applied. My previous Nema 23's shafts had resistance when wired BP and locked up solid when power was applied. I did check this with the supplier but they confirmed that's what these Nema 34's do. Was tempted to replace them all with another make but ran out of cash to do so.

Oh, and not quite out of hair yet but getting close, the bald patch on the top of my head is getting larger :)

That's the same motors I run. Difference is I'm running Gecko drives, until we installed the 4:1 drive reduction I had issues with the z axis pulling into the job sometimes with upcut bits. I also had issues that if you reached over the z axis to grab the dust tube off sometimes if you leant on the top of the axis it would drop. All is well now with the drive reduction.

That isn't right.... the shaft should lock-up solid.

IMHO, unless broken, all brand/make stepper motors makes no different with MM.

Sound very much like a bad motor. Unlucky :( ....

Ken, not broken, all the motors are wired the same way and all act in the same way. When I queried the wiring with AusXMods he confirmed the the shafts would NOT lock up on these motors and I even double checked with MS Motor themselves.

Thanks clarson66, sounds like I should just pull my finger out and get my belt drives done. They'll have to be MDF or plywood initially though, no way I could cut ali at this stage.

24T pinion will give 25% more torque then 30T, should improve thing a tat. and cost very little time & money.

Did you do motor tuning for Z? you get loose steps?

Was just outside having a smoke and thinking the same thing Ken, will price some 24T's on Monday.

Z motor tuned the same as all the rest, no lost steps if I am very careful plunging, too aggressive and lots of lost steps.

the "free" thing to do now is re-tune the motor to lower acceleration & velocity, write a short G-code doing repetitive up-down for the tuning purpose.
At least get you to continue cutting.

Some hybrid motors will spin free with no resistance without power, some with achieve detent torque when you spin freehand faster then turn with resistance others will not like to be turned at all. Depends on the manufacturer. As far as the Z motor running hotter while running, mine is always 10°C hotter than the other axes. Every driver is different on how they function. AMCI driver will cook eggs on 100% idle reduction but at 50 it is only a little above room temperature. Gecko 203V drive barely heat the motor at all at idle. That is how my motors are.

You said you swapped the motor drivers. Just be thorough, put the suspect motor on the Y drive and have g-code run only it (the Y axis) and let it sit idle to rule out some other hidden troubles. Lets see if the problem moves.

Thanks for the info Pete, appreciated.

Got some rubbish to get rid of then will do the motor swap. Will report back with the results. Will also do a quick video of the Z as it currently sits basically bouncing at any resistance.

Overall I am pretty happy with the machine, its just these niggly bits that annoy me :)

Found something this morning, the controller is the one heating the motor up, I connected the Z controller to the Y motor and vice versa, now the Y motor is really warm from sitting for an hour or so and the Z motor is stone cold.

The Z however is *still* stalling under *any* pushback so I will very carefully cut out a belt drive from MDF to chuck on the Z and see what happens.

Later this avo I will recheck the settings on the Z controller (now on the Y) to find out why the attached motor is heating up at idle.

I would recommend belt reduction for the axis. Will give it more strength. I have a PK296-F4.5A 440 in-oz wire parallel with a 4:1 reduction. I haven't had any problem. I give the spec so you can relate to your motor to see what others are using and not to tell you what to use.

Thanks again Pete, will definitely move on the belt reduction now for the Z. I would think that 640 Oz-in/2.2Mh wired parallel would be better than it is, my drives will be 3:1 to start with until I see how it performs.

What is strange is Automation Technologies has a motor with the same part number but it is wired differently than the MS Motor of the same number. Don't know where Auto Tech get theirs from but must be another supplier. Anyhoo, I have what I have and will make them better by belt reduction :)

Cheers

Haven't got around to building my belt drives yet but have cured the Z heating issue. The controller was set to 100% current at idle even though I had the dip switches set. A quick adjustment via software fixed that.

See, sometimes a break is all that is needed

Yup, correct on that one. Still haven't got my Z to lift the Y yet though, even after swapping motors between the Z and the Y :)

I contacted the supplier re my motor woes and he thinks (as I do) there is something definitely wrong. Currently working through a few things to report back to him.

For reference, here's my Z being a jack hammer...

http://youtu.be/nQJ-SfYNpuU

Could had been too strong spring for the y car. Nothing much to get concern with..
BTW,did you set the correct Max. Current for Z?
Or you should consider parallel coil for higher torque.

Are you sure that the stepper is not jumping the pinion on the rack. That is what it sounds like.

Ken

does this without the Z strut on too. Yes on the amps, 6.4 on the controllers. I even disconnected all other drives and ran only the Z and it still does this. Oh, and they are already wired parallel, push comes to shove I could go serial but would need to replace my power supply as serial would be 8.8 mH

Just went and checked that Pete, no skipping of the stepper. the noise seems to be the motor pulsing but not stalling