EEVblog #327 - Makerbot Replicator Troubleshooting

[EEVblog]

Dave.

[hlavac]

I totally noticed that missing screws the moment you were showing how the motor is turning

[Short Circuit]

Maybe intersting link for the makers of the printer;
http://www.nylok.com.tw/e_p/NYLOK%20PATCH.html

Nice threadlocking without messy stuff or chances to forget.

Costed me £163 for orders of 10k small screws, 3 years ago.

[ludzinc]

Wow.

Grub screws suck.  For the price you pay for a 'bot, why aren't the gears keyed?

[johnnyfp]

$1800 is cheap! These guys aren't Brother or Canon, they sell peanut quantities compared to the large printer companies. And just don't have the buying power to get custom made slotted rods for a price that won't affect the end user.

If you look at commercial based 3d printers, they cost a small fortune and some of these are no better using grub screws and such.

If you look at Ultimakers, or Mendal repraps (comercially made versions) they are all the same. Even an UP! has grubs.

[EEVblog]

If you look at commercial based 3d printers, they cost a small fortune and some of these are no better using grub screws and such.
If you look at Ultimakers, or Mendal repraps (comercially made versions) they are all the same. Even an UP! has grubs.

That's for the clarification, I wondered if that was the case.

Dave.

[TerminalJack505]

Those shafts need to have a flat or knurled surface for those grub screws to tighten against.  Otherwise you can have problems getting those to loosen-up once they've been in there for a while.

[nitro2k01]

Good to hear it wasn't permanently b0rken, at least.

[ecat]

"A set screw is usually insufficient so we need a keyway"



And a matching slot on the pulley:


I guess this is how it used to be done. Indeed, it may still be this way on heavy machinery, or when the expense of the machining operations can be justified.

The big printer guys appear to use what I assume to be a cheaper solution, friction or interference fit. The gear/pulley is such a tight fit on the shaft that no additional slot or screw is required in normal use. Check out the steppers from, say, a Photo Copier tear down, I'm sure most of the fittings are simply a very tight push fit.

Dave,
If you think a poorly judged Home operation is a worry on a little 3D printer, you should get hold of a big CNC'd milling machine and try the same thing. Ouch!
 

[Erwin Ried]

I felt a bit disappointed when I saw they will not do a "kit" version of The replicator.

Assembling my last makerbot was the most fun part of the process and it always printed perfectly, several kilos of abs plastic up to date. In think in this kind of product I will not trust 100% on something not assembled by me.

[richcj10]

adding a indent on the shaft should cost little....
Hell, they could use a drill press with a mill bit and achieve what is required...
To think that the set screws would stay in place on a smooth shaft like that at any length of time is stupid...

[robrenz]

There is a reason that they don't have flats or keys or indents in the shaft that align with the setscrews of the pulleys. The squareness of the X and Y axis is controlled by the rotational alignment of the teeth of the timing pulleys to each other. If you are one pitch off on that you are out of square by one belt pitch over the spacing between the belts.  And that is if everything else engaging the belts on the in-out axis (Y?) was perfectly symmetrical.  Stock pulleys also do not have the setscrews or keys in any relationship to the teeth of the pulleys. I am not saying there is not a better way to do what they are doing, there are many.  It's just not as simple to fix as some think it is.

[KTP]

What robrenz said is correct.  The way the design axis is aligned, you have to have that infinite adjustment on the pulley orientation on the shaft.

The very best thing to use that would keep this ability is a helical clamp pulley.

[EEVblog]

What robrenz said is correct.  The way the design axis is aligned, you have to have that infinite adjustment on the pulley orientation on the shaft.

The very best thing to use that would keep this ability is a helical clamp pulley.

Ok, but surely you could use it on the motors at least? and maybe one end of the axis as well, having the other end infinite?
That would surely improve the reliability an order or more?

Dave.

[KTP]

What robrenz said is correct.  The way the design axis is aligned, you have to have that infinite adjustment on the pulley orientation on the shaft.

The very best thing to use that would keep this ability is a helical clamp pulley.

Ok, but surely you could use it on the motors at least? and maybe one end of the axis as well, having the other end infinite?
That would surely improve the reliability an order or more?

Dave.

I agree.  Also, the motor pulley has by far the most torque on it of all the pulleys in the system, possibly the most vibration also.  At the very least, grinding two flat spots on the motor shaft for the set screws (the correct term for non Aussie) would provide a much more reliable grip.  A little loctite wouldn't hurt either.

Of course this would be a better platform (if I ever get around to finishing it I may add a maker extruding head)

[robrenz]

Ok, but surely you could use it on the motors at least? and maybe one end of the axis as well, having the other end infinite?
That would surely improve the reliability an order or more?

Dave.

I completely agree.  Also larger pulley hub diameters would allow a longer grub screw (set screw for us yanks ) that would have a deeper hex socket that is less prone to stripping out.

[SeanB]

Loctite 603 will hold it even if the setscrew falls out and is lost. I use it a lot, even if removal involves a heat gun afterwards to persuade it to let go. Has very nice gap filling ability, perfect for those assemblies with less than stellar fit.

Keyways work, but for the ultimate you need to use a drill and a taper reamer, so as to put a taper pin in. Holds essentially forever, and generally the failure mode is shearing of the steel taper pin, and only then if you have applied way too much torque for the shaft. Generally though not really adjustable after initial fitting, unless you have a new shaft. When I bought my reamers the metric one was $50, the imperial one was $5, for some reason, and of course the metric was out of stock. Only difference is the taper, 1:10 for metric, 1:12 for imperial. For low stress I often use the metric pins in the imperial hole, as the imperial pins are hard to get, and generally are special order, while the metric are off the shelf in assorted sizes. Gentle persuasion is the key, that is the name of the hammer I use to put them in. Getting them out after a few years often involved the heat gun and a drift with a much bigger hammer, or drill them out.

[JoannaK]

Ok, but surely you could use it on the motors at least? and maybe one end of the axis as well, having the other end infinite?
That would surely improve the reliability an order or more?

Dave.

I completely agree.  Also larger pulley hub diameters would allow a longer grub screw (set screw for us yanks ) that would have a deeper hex socket that is less prone to stripping out.

Looks like they need some help on mechanical design, grub screws on round axels (and too many screws/axels/belts in first place) ain't futureproof design. There will be risk on slippage and in time it'll lead to some alignment problems with Y-direction.

Dave: you are right that there should be some kind of mantenance manual .. (tighten these screws, add some oil etc)

[EEVblog]

Dave: you are right that there should be some kind of mantenance manual .. (tighten these screws, add some oil etc)

The include some lube in the box!

Dave.

[Things]

Dave, you could probably try something as simple as even putting some teflon tape on the grub screws. Should help hold them a bit better with the vibrations from the motor.

I've homebuilt myself a laser cutter too, and the damn grub screws were falling out all over the place! Bit of teflon tape fixed em right up. Loctite would work too I suppose, but is a little more permanent, and you'd have to be careful to not strip the heads if you ever needed to remove them again.