Hey Y’all,
I hope everyone is having a great Friday, I apologize if this has been discussed on here before, I searched around and couldn’t find anything. I’ve been using my Shapeoko 3 XXL for a little more than a year with pretty much no maintenance or adjustments after I finished building. Earlier this week, I decided to order the new HDZ upgrade in the hope of cutting aluminum faster. Now that my machine is getting so fancy, I think it’s time to really get it dialed in. I ordered a dial indicator to level off all of the rails, and a spoil board flattening bit to machine level my work surface. I already have the machine squared up perfectly. The last obstacle seems to be the GT2 belts. Every discussion that I’ve seen about tensioning them uses really vague language like “tight enough to slip a finger under” or “a quarter turn past what feels like too tight”. First of all, how important is it to have the belts properly tensioned? I’ve been using the “finger under the belt” method and haven’t had any issues, but I’m afraid of leaving precision on the table, especially after a $450 upgrade haha. Secondly, is there a more precise way to tension them? Is there some sort of tool I can buy to measure the tension while I’m making adjustments? Or is it not even worth the effort?
Lastly, while I’m fiddling and adjusting, is there anything else I should be doing to get my machine in tip top shape? I’ve just been following along with Winston’s “basic tuning” video, but if anyone else has other suggestions I’d love to hear them.
The folks on the other side of the house use spring gauges such as one would use for weighing fish.
When I first set up my SO3 I used the weight of the machine to tension the belts which seemed to work well, but that was with the old sliding motor mount tension system — I still do this on the Y-axis belts, just use a luggage scale, lift up until it registers 40 lbs. or so and then tighten the motor into place.
I noted the tune I was getting on the Z-axis belts, but that doesn’t apply since you have the HDZ.
The other thing I’d suggest is if you don’t have 9mm Gates-branded belts, get them (I bought mine from SDP/SI) — or you could try one of the other core materials — steel is popular (though I worry about the bend radius), or Kevlar instead of fiberglass.
Amazing! Thanks for the reply! I’ll order those gates branded belts. Just for clarity, are you saying that you loosen the motor from its mount, attach the luggage scale to the motor, pull up, and then tighten it when it reads 40 pounds? Also, is 40 pounds the ideal tension for all three X and Y axis belts? Or do they differ. Thanks again, have a great evening.
Unfortunately, this technique only works if you have the old sliding motor mounts — doesn’t work on the new machines with PEM nuts for mounting the motors. For them, I think the best thing to do is to start in the center, then move the machine to one end, loosen and retension the belts, then repeat on the other end — I find it easier to get tension on the belts that way. Careful not to bend the motor shaft.
Yes, I pull on the scale until it reads 40 lbs., then tension the belts.
Not 100% convinced the Gates-branded belts are markedly better — for the price difference they ought to be, YMMV.
I like my belts at tight as I can reasonably get them. I always had a problem with getting the holder on once I got it overlapped where I wanted it then I figured out a way that has worked for me. First I loosen 1 end a lot (where the bolt is only attached by 1 turn) then I clamp the belts to the rail on that end so the teeth are interlocked and can’t slip. Then I go to the other end and adjust to where I can barely get the bolt started and I tighten it down, go back to the other end and tighten the bolt (with clamp still on it) and once I can’t move it anymore I remove the clamp but (most important) press down firmly on the overlapping belt so the teeth don’t slip and finish fighting it.
This makes the belts easy to do and make it as tight as is reasonable.
I bought a set of steel cored belts but have not installed them yet. When I do I plan on using this same method.
I also thought there should be an easier way to work the tension. I drew up a sketch of what I had in mind and have just not had the time to work with it. You might take a look at it and see if it would work for you. It is free gratis! If you try it and it does work, let the forum know. I won’t get back to my system for another month or two - trying to get my shop in much better order than being a junk pile.
Here is an issue I can foresee with your concept: the V wheels use the whole track, in fact the belt clip, needs to be tight and in the right place to ensure proper travel over the whole track, Those clips are very close to the place where the V wheel travels. I’ve had to move the clip a few mm so I could get full travel and clear the V wheel as it would bump into the clip.
You could indicate a pulley when tensioning and measure/match acceptable deflection? I haven’t tried it but it sounds cool.
The stock belts are tough because they give a decent amount, it’s much more of a feel thing.
While steel core sounds scary, its proven an acceptable life and I haven’t seen the need to adjust microsteps. They can do damage to your aluminum pulleys if run long enough with a cord/s broken but its easy to see during a machine inspection. Also they dont stretch as much and that means the tension range is smaller.
You should think about chip protection if you haven’t already. A clean V wheel is a reliable V wheel.
Mr Morris - How did you clamp the belts to to rail to prevent them slipping? I am at the point where I have my machine almost assembled and am having a problem getting the belts tightened. Thanks!
First thank you Will for providing links to the part numbers. Similar question as Michael Oakley stated, I am going to purchase some extra belts so I have them on hand for when the time comes. But I am wondering on the second link for the timing pulley with the 2mm GT pitch, Does the Shapeoko stock timing pulley not work with the belts you referenced? or are stock timing pulleys not aluminum? Just curious and not a big deal to add to the cart , do I just need two of the timing pulleys for X &Y ( i have an HDZ) sorry if this was answered elsewhere as I am not at home to look at my machine
“6.25 lb / 2.8kg” (for 6.35mm width belts) -> implies 25lbs or 11.2kg (109.8 N, you mass/force confusing metric savages), and what appears to be linear scaling from the same spec as the above two
So for our 9mm belts, I think the working spec tension should be (9mm/25.4mm) * 25lbs = 8.86 lbs or 39.4N.
Does that sound right? That’s a bit more than the weight of a gallon of water. I could believe it, but my experience, like yours, says I probably use more.
The machines seem to work better when tensioned more than the specification calls for.
This idea grew out of using the weight of the machine to tension the belts with the old style sliding motor mount tension system — it seemed to work, I just carried forward 40 lbs. as a reasonable compromise between the weight of the machine and what I can reasonably lift/hold with one hand while tightening a bolt with the other.
I’ll have to figure out what my tension is with my fish scale when I find some extra belt. I tried averaging out the feel of all my belts, then looked at where they stood with my torque wrench - about 10 inch-lbs. In retrospect, tension now feels muuch more consistent after I ran the wrench around.
I tried calculating the equivalent tension based on the torque, but the calculation’s hilariously off, by ~order of magnitude:
T=K * F * d, where T is torque, K is unitless “nut factor” (heh), F is axial force, and d is the diameter of the screw.
Torque in my case is 10 in-lbs, typical K value for a sorta slick material is like 0.2, and diameter of our M5x10 Socket Head Cap Screws is 5mm. F = T/Kd = (10 in-lbs) / ((0.2)(5mm)) = 254 lbs lol
I think the cantilevered setup on the tensioner is jacking friction through the roof and K is probably more like ~1 in this situation (and dynamic! threads being less jacked as the bracket nears fully-tight). Oh well, I’ll grab some spare belt to measure sometime, and we’ll see. Got some steel belt on the way, anyway.
Early/launch edition machines came with 6mm belts on X and Y in addition to the Z (unfortunately, endless belts are 6mm wide at most), so the pulleys on machines made prior to summer 2016 would need to be replaced — machines since then come with 10mm wide pulleys on the X and Y which fit 9mm wide belts.
