Smooth Idler Pulleys

Questions, Suggestions, Tips, Etc

Re: Smooth Idler Pulleys

Postby dirktheeng » Sat Jul 02, 2011 8:49 am

Bart,

I did think of a "potential" problem with the new idler pulley setup. In the current design, the bearings provide a large area to distribute the load on the shaft to the plastic which reduces/eliminates any concern of deforming the plastic under load. In the new design, the contact area of the shaft to plastic is very much reduced and is eaven further reduced by the fact that the shaft is a threaded machine screw. I am concerned that the threads will bite into the plastic, deform it and miss-align the shaft as we load it up to keep the belts under nice tension. It may help to either press fit a bushing in place or thread the hole with the same thread that the machine screw is.

We can give it a shot and see. I am also curious about the cost comparison to replacing the bolt with the shaft like I did on my machine. Replacing the shaft with a polished down precision shaft only costs about $0.75 per idler. I dont' know how much those derlin smooth pulleys cost, but I'd venture a guess that they are close. You can further reduce the cost of the precision shafting by buying from a vendor that isn't mc master (price mark up) and buying in bulk. It is seriously about 2 minutes worth of work to polish the shaft down to make them fit into the existing setup and I have zero slop and no wobble. I chucked the shaft into my electric drill and used some fine grit paper to polish the end down until I could barely get the bearing on. I put a dab of super glue on the end and it was fine (though I didn't really need that as the press fit was tight enough).
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Re: Smooth Idler Pulleys

Postby dirktheeng » Tue Jul 05, 2011 11:20 pm

I recieved the new v-groove bearings, smooth idler pulleys, and a few spacers. I'm not exactly sure how I am suppoted to replace the v-groove bearings as the spacers need to be adjusted.

I recieved 13 spacers (look like precision washers). I need to keep the plastic spacers on the gantry because I still have to use the ecentric nut. This means I have to move one of the y axis v rails over fairly significantly at least 1/4".

There is also quite a bit of space needed for the smooth idler pulleys to be in the same place. See the picture below:

DSCN3592.JPG
Flat Pulley in rough place


This pic shows the the new v-groove bearing next to the old ones. The new bearing is just sitting on the rail in back of the installed ones.

I'm going to try to install these tonight and post some pics. What I am concerned about most is keeping the gantry cart at roughly the same height off the rails as there isn't much adjustment to be had by moving the laser up and down (it will miss the mirrors). Without different spacers, the gantry car will sit high. I'll measure b/4 and after install.
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Re: Smooth Idler Pulleys

Postby bdring » Tue Jul 05, 2011 11:34 pm

I know all this.

I sent the v groove wheels for you to play with. I do not intend for them to ever be used on the 2.x laser. They are not needed. The smooth idler pulley will be integrated into the design once I get the right spacers. I would have sent them if I had them. Maybe I jumped the gun on sending you parts.

Bart
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Re: Smooth Idler Pulleys

Postby dirktheeng » Wed Jul 06, 2011 12:24 am

bdring wrote:I know all this.

I sent the v groove wheels for you to play with. I do not intend for them to ever be used on the 2.x laser. They are not needed. The smooth idler pulley will be integrated into the design once I get the right spacers. I would have sent them if I had them. Maybe I jumped the gun on sending you parts.

Bart


Oh... that makes sense :oops: :P I misunderstood from some of the posts. Anyhow, I put the new v-groove bearings on the gantry car and tried them out. Here are a picture:

DSCN3596.JPG
New V-groove bearings on laser cart


The new v-groove bearings add 2.35mm to the height to the rig. As bart said, these aren't meant to be used for the 2.x design.

The new bearings are very nice. The seem very strong in comparison. The plastic shielded bearings have more rolling resistance than the 2.X bearings. Also, be sure to use one of the metal spacers b/t the bearings. They need that in order to be able to tighten the bolt that holds it on, otherwise they bind. the spacers seem to work very well and fit nicely. They will definately take rotational slop out of the equation. I think that spacer in the middle needs to be very carefully matched to the spacer that goes between the bearings. You want the spacer between the bearings to be a few thousandths of an inch smaller than the spacer aroudn the rim of the derlin wheel. That way, the bearins are pre-loaded sligtly so that it removes maximal slop. This is a fine game to play because if it is too much difference, the bearings will bind. Without this we will have about the same lateral slop in the bearings as if we only used 1 bearing.
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First smooth idler pulley install

Postby dirktheeng » Wed Jul 06, 2011 3:19 am

All,

I replaced the X axis idler with a smooth pulley assembly. To make up the space to keep it aligned, I used 5 spacers that are 1mm thick and 1 of the 1.4 mm washers. Actually, one of the plastic spacers that were used in the lid hold up were about the right size. I wanted to use the metal spacers because it would add some stiffness to the design. I put the larger metal washers on either side of the plastic mount to add some more support.

The hole bart made in the plastic was just undersized enough that you had to screw the machine screw into it, which was really good because it ensured good contact and alignment.

Here's a pic of the setup.

DSCN3598.JPG
Smooth Idler setup


In my opinion, this is a huge improvement, even over putting a precision shaft in place. The shaft was fine, but the plastic pulley on the shaft was one of the cheaper ones and not precision made so there was minimal belt wobble even still. This however, is VERY smooth and the belt doesn't even move side to size when the cart travels. By sandwiching the plastic part with larger washers, the connection is very solid and can take a lot of stress. By undersizing the hole, the shaft is aligned well. Over all, I am very happy with this. I like it better than my shaft setup.

BTW, an upgrade kit will have to include M5 machine screws and nuts. I found that the x axis idler could use a 35mm shaft and be just fine (I reused the screw from the lid holder I took off). I was able to get a flat and lock washer on the back with a nut and the end just barely protrudes. The other shafts are going to need 40mm screws.

This is a great upgrade. When I move the car by hand, there is absolutely no pitch change in the motor and everything feels nice and balanced and smooth! You can sight down the belt and everything is very nice and strait!

This is great! I can't wait to get them on my y axis. I don't have enough 1mm spacers to properly space the bearings out from the plastic holder, so I will probalby use the 2 plastic spacers that came from the lid support.

I will try to get that done tomorrow and report, but I am expecting really good stuff.
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Re: Smooth Idler Pulleys

Postby bdring » Wed Jul 06, 2011 12:37 pm

#10 washer should work well as spacers and they are easy to find at the hardware store. Save the 1mm shim washers to use between the bearings. The pulley was made slightly wider that the belt so the spacing does not need to be perfect. Rounding to the nearest 1/16" inch is fine.

I I forgot that the Z might be able to use a smooth idler too. It won't really benefit from it much, but it would be nice to have them everywhere. It always kind of rubs me the wrong way to run the back of a belt over a pulley anyway. The trick is, there is not much room for a screw head under there. I would need to use a low profile screw.

The cost is about a wash on the change over and the brackets are a little faster to make now so I don't think it will affect any kit prices. I should be able to start shipping these as standard equipment by the end of next week.
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Re: Smooth Idler Pulleys

Postby dirktheeng » Thu Jul 07, 2011 12:08 am

Sure thing... I put 3 No 10 washers on and left one of the 1mm spacers in just to make sure nothing rubbed. I also flipped the pulley around so that the overhanging part is facing outwards. The belt rides so nicely now, it only moves on the pulley ever so slightly and there is no wobble at all. This is a really great solution!

I'd go for a smooth idler on the z axis as well. Looking at my current rig, there is probably enough room to get a cap screw down on the bottom of the pulley if the new plastic holder doesn't hang down too much. I think the 1/4" plastic could work for this as there really isn't much strain to take and it isn't critical to have it aligned. What do you think?
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Re: Smooth Idler Pulleys

Postby bdring » Thu Jul 07, 2011 12:14 am

My models says it won't fit even with a low profile head. You could go with one bearing. Then a standard screw with fit. I think one bearing is still better than what we have.
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Re: Smooth Idler Pulleys

Postby dirktheeng » Thu Jul 07, 2011 12:24 am

Bart,

Here's a pic that shows that it will fit, don't use a washer on the sholder of the cap screw. The bearing doesn't need a washer as the head covers the inner race and a dab of thread locker will take care of any concern about lostening rather than using a split washer. You can actually gain even more clearance by flipping the timing pulley on the threaded rod so the belt is up further.

DSCN3599.JPG
z smooth idler pulley rough position


It also doesn't matter if the cap screw head touches the botom pannel because it doesn't spin. Also, notice the orientation of the smooth idler... the protruding side is down to gain maximum clearance. It is dificult to show a good angle here, but there is actually room to move this up a slight bit as is.
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Re: Smooth Idler Pulleys

Postby bdring » Thu Jul 07, 2011 12:31 am

Is the shim between the bearings?
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