missed steps

[martin54]

2 new nema34 motors turned up today, new motors are same frame size & depth as original motors but are more powerful & require a larger power supply.
Next problem was that the motors drive through a gearbox & having pulled the gear wheel off the motor spindle I discovered that the original motor spindle is round with no flat & relies on an interference fit on the shaft. Probably now going to have to drill & tap the gear & use the flat on the new motor spindle to stop it turning unless anyone knows of another way to do it, hopefully get that done next week sometime depending on how I feel & how much work I have to get done.

[Leo]

Sounds like you are getting the problem narrowed down.

It will be a grand day when you say the problem is goon for good.

[zeeway]

2 new nema34 motors turned up today, new motors are same frame size & depth as original motors but are more powerful & require a larger power supply.
Next problem was that the motors drive through a gearbox & having pulled the gear wheel off the motor spindle I discovered that the original motor spindle is round with no flat & relies on an interference fit on the shaft. Probably now going to have to drill & tap the gear & use the flat on the new motor spindle to stop it turning unless anyone knows of another way to do it, hopefully get that done next week sometime depending on how I feel & how much work I have to get done.

If you use a set screw with Locktite torqued properly against a flat, you will have a very dependable connection. You might check to see if any of the gears slipped previously - this could also have been a source of "missing" steps.

Angie

[martin54]

Checked the gearing for damage/slipping before buying new motors so pretty sure it's not a factor, only problem with drilling & tapping the gears is that they will probably be hardened so may have to either try & source new gears or find a local engineering company that could do it for me.

[rbraeking]

I have learned the school of hard knocks that missing steps can be caused by a number of things:
1. Underpowered motors
2. too much microstepping. Keep microstepping to a minimum as the power curve on stepper motors drops off dramatically when microstepping. Mechanical speed reduction not only allows less microstepping it also gives the motor more mechanical advantage.
3. Mechanical resistance.
4. too much current. My new stepper for my y axis was really noisy and inaccurate at the amperage setting recommended on the data sheet. When I reduced amperage the motor quieted down and accuracy improved.
5. Kernel speed set too low.

Bob

[martin54]

OK so as I said the new motors had arrived but there were no markings on them what so ever & no data sheet with them, I emailed the seller to ask for a data sheet & got a reply saying that I should use their drivers & a link to where I could buy them. Emailed the seller again & explained that I already had drivers & power supply & just needed the data sheet for the motors for voltage & current ratings.
Seller sent me a data sheet & this is where I started to get a bit annoyed, motors I had ordered were 420oz which is just under 3Nm (2.965) but the manufacturers data sheet had them rated at 2.2Nm which is 311oz seller told me that it was OK & max was 3Nm to which I replied that even if they were capable of 3Nm this would shorten motor life if operating outwith manufacturers guidelines.
Answer to that was "To be honest this is our special order motor & will run at 3Nm without reduction of motor life"

I could have bought 2.2Nm motors from a lot of other sellers cheaper than these motors but would the motors I received actually have been 2.2Nm or a lower power motor that could do 2.2Nm. ??

[PaulRowntree]

I have learned the school of hard knocks that missing steps can be caused by a number of things:

5. Kernel speed set too low.

Bob

Bob, I had never heard this. Do you know why kernel speed has this effect?

[rbraeking]

if you have a motor set to 12800 pulses per inch and try to drive it at over 200 inches per minute a 25mhz kernel speed won't be able to keep up. Mach3 is supposed to warn you but it does not always do so.

[martin54]

Quick update, borrowed a couple of motors from someone I know who had them sitting about waiting for him to get round to using them for a project so has given me the chance to test the machine while I am waiting for the ebay seller I bought motors from to sort things out.

Fitted the 2 motors & power supply, did a bit of retuning on the drivers & within mach3 to make sure everything was set up correctly & tried a test cut cutting air, machine ran really well so next test was actually cutting something, again worked really well & parked itself exactly where it should have done on completion. Did a few more tests & everything now seems to be working great.

Now I just need to learn how to use the thing properly, long term I will look at manufacturing a new z axis for it, the z axis runs on fairly small unsupported rail & is driven via a trapezoidal lead screw. That set up will get replaced with either profile rail or supported rail (cost dependant) plus I already have a 1605 ballscrew, ball nut & bearings that I bought for the machine I was going to build.
Oh & I will also need to look at dust extraction as well, some sort of dust shoe for it. Would also like to look at some sort of vacuum table or part table as well but that would take a fair bit of figuring out, don't want to build something to sit on top of the T slot table because the gantry is only about 60mm above the table to start with.

[rbraeking]

I am setting up vacuum this weekend. 1.5 inch pvc under the table and 6 zones cut 1/4 x 3/8 deep pattern of lines on 2 inch centers. My shop vac has enough suck to hold down a sheet of foam or plywood. I block off un-used zones with rubber stoppers ($18.00) rather than a valve manifold ($120.00)The plan is to do the first cut with vacuum hold down then, knowing the location of the waste, screw down the sheet to finish. If I do the first cut with a down cut bit and the second thru cut with an upcut I should get a good crisp edge. I'll keep you posted as I will be cutting a pattern for an interior designer that is pretty intricate thru cutting on 5.2mm high density fiberboard (hdf). I have had too much work to install my new z but it will be running on 2 20mm round/supported rails with 4 bearings. I will be able to fine tune the perpendicularity (is that a word?) by mounting the z on a pivot in the y direction and shimming the router clamps in the x direction.

Shop Bot has an excellent dust collector that fits a water cooled spindle.

Bob