[cowanrg]

I got done with the mechanical conversion on my PM30 awhile back, and when I started using it, I noticed that the spindle and head were getting REALLY hot. It seemed like it was the spindle bearings as well as the intermediate gears. There was also some noise. I decided to go straight to a belt drive system for the spindle.

First, I replaced the tapered roller bearings with angular contact bearings, and re-greased everything. It ran a lot cooler, although the intermediate gears still had quite a bit of noise.

Next, I made some rails, got some pulleys, etc. I'm using a GT2 belt and pulleys from SDP-SI. I just machined off the hubs, bored out the centers, etc to create 2 stacked pulleys. I'm doing a 44:38 ration and a 24:56 ratio for high/low. This should give me around 6500 and 2500 RPM.

Everything went well, but when I went to run it for the first time, it didn't sound very smooth. I messed up the bore on the back pulley, so that's not helping. I will either need to shim it or just redo it from scratch. The other issue is that the belt keeps slipping down. No matter what I do, the belt wants to fall down and ride on top of the casting. If I use the top pulleys, it rides down until it hits the other pulley. Tight or loose, the belt just wants to ride at the very bottom of the pulley until it hits something. Thoughts? Here's the setup in solidworks:

[bhurts]

You may need to shim the motor mount to get things aligned properly. Also usually one set of gears is flanged to help with alignment.

Ben

[cowanrg]

Ah OK, so the motor pulley set might not be parallel to the spindle set?

unfortunately, none of the gears had the option for a flange :-/

[SCzEngrgGroup]

You need to have at least one flanged pulley on the belt, to keep it from walking off the pulleys.

Regards,
Ray L.

[hoss2006]

You need to have at least one flanged pulley on the belt, to keep it from walking off the pulleys.

Regards,
Ray L.

No you don't, it can help but my first belt drive was a similar dual pulley setup with no flanges and it worked perfectly well.
You have to have them aligned properly or even ones with flanges will rub the belt on one side too much.
Hoss

[bhurts]

Yes the motor pulleys are not parallel to the spindle set. The only option is to shim the motor mount either in front of the motor or behind it. Where depends on which way the pulley is walking.

If the picture you posted is the same base plate for the motor as what's on the machine you can remake that part without the round sides. Then drill and tap for a set screw at each corner. That will make it easy to make alignments to the spindle.

Ben

[CRO-WD40]

Everything went well, but when I went to run it for the first time, it didn't sound very smooth. I messed up the bore on the back pulley, so that's not helping.

sleeve it or redo.. it wont help with centricity of shaft to pulley if the bore is worn.

I will either need to shim it or just redo it from scratch. The other issue is that the belt keeps slipping down. No matter what I do, the belt wants to fall down and ride on top of the casting. If I use the top pulleys, it rides down until it hits the other pulley. Tight or loose, the belt just wants to ride at the very bottom of the pulley until it hits something. Thoughts?

You can shim the motor equaly so you can fit the straight edge inside to measure whats not parallel.

Then remove those shims and add them where they are needed. Something like this



also check if the shafts are straight with a dial indicator, spindle shaft and motor shaft, just to be shure that something wasnt bent during bearing replacement.

[cowanrg]

cool, this is good information and pretty much what I expected. I will first try to shim the motor mount forward/backward to see if I can get the belt riding in the right spot. Then I need to address the bore on the motor pulley. It's definitely not concentric. I should have done them on a lathe, but I don't have a lathe, yet.

CRO-WD40, can you explain what you mean:

"You can shim the motor equaly so you can fit the straight edge inside to measure whats not parallel.

Then remove those shims and add them where they are needed."

[cowanrg]

I messed with it a bit more. By tweaking the 'angle' of the motor, I was able to get the belt to ride where I wanted. It's a bit tricky and will take some shimming, but it's doable.

Unfortunately, it looks like my pulleys are just not all that concentric. I tried my best to center the bores on the mill, but it seems I have failed. Is there a better way to do this or do I just need a lathe?

I used my test indicator mounted in the spindle, and spun it around the inside bore until it read 0 when spun around. It fluttered around a bit (maybe +- 1 thousandth). Then I rough machined the bore with an endmill and then cleaned it up with a boring head/bar. That seemed to be the best way to do it, but I didn't get them very well-centered.

I can run everything at low RPMs, and it's alright, but as soon as I go faster, there's some rattle and noise, and it's from the out-of-center pulleys, you can see them jumping around a bit. Also, I can't tighten the belt too much or else I get a lot of noise too. But, as slow RPMs (maybe 1-2k?) and a somewhat loose belt, things are OK.

I kinda though I'd be able to do better with the pulleys, but it looks like I'll have to start over from scratch. is there any saving them?

[library]

You pretty much *need* a lathe to bore the pulleys out properly. I was in the same situation you are with just a mill. I used a coaxial indicator to dial in the exact center and then a boring head to bore it out. Mine was still offcentered a little. I used it as the excuse to buy the lathe. The one I bored out on the lathe was absolutely perfect.

You could save the old pulleys by boring them larger on a lathe and then sleeving them but I would just buy another set of pulleys. See, if you'd bought the lathe already you could have saved the $100 in wasted pulleys, that's the way I explained it to my wife.

[CRO-WD40]

cool, this is good information and pretty much what I expected. I will first try to shim the motor mount forward/backward to see if I can get the belt riding in the right spot. Then I need to address the bore on the motor pulley. It's definitely not concentric. I should have done them on a lathe, but I don't have a lathe, yet.

CRO-WD40, can you explain what you mean:

"You can shim the motor equaly so you can fit the straight edge inside to measure whats not parallel.

Then remove those shims and add them where they are needed."

the picture you posted.... in that configuration you can't place a straight edge to measure parallelism because there is no room between the pulleys.

If you shim the motor by lets say 20mm equally on all sides to lift it so you have enough room to slip in straight edge in between the pulleys.
You press the straight edge on the side of one pulley and measure the gap on the other pulley with feeler gauge.

Then you remove those 20mm and add required shims that you measured.

[cowanrg]

You pretty much *need* a lathe to bore the pulleys out properly. I was in the same situation you are with just a mill. I used a coaxial indicator to dial in the exact center and then a boring head to bore it out. Mine was still offcentered a little. I used it as the excuse to buy the lathe. The one I bored out on the lathe was absolutely perfect.

You could save the old pulleys by boring them larger on a lathe and then sleeving them but I would just buy another set of pulleys. See, if you'd bought the lathe already you could have saved the $100 in wasted pulleys, that's the way I explained it to my wife.

Even though this is bad news, it's good to know the right way to do it. If someone told me "it's super easy to get right on a mill", I would hesitate trying again... But it looks like I just need to get a lathe. That's not a big deal, I've been wanting to get one for awhile, just not quite yet :-)

I think I'll just get a lathe and see if that helps. Thanks!

[bhurts]

I will play devils advocate here. It should be no problem to bore the pulley on the mill. You have to indicate the bore like you did for center. You also have to indicate the bore in perpendicular to the x and y so you know it is straight up and down in both directions.

Ben

[handlewanker]

Hi.....just another 2 cents worth, but more to the point........if you want to bore the pulley on a mill (no lathe etc) you have to indicate off the Outside diam of the pulley and across the face too.

Always, when you set something up to be concentric, you should choose the biggest face to indicate off of.

Even in a lathe you set the OD to run true and at the same time across the face in two planes at 90 deg to each other.

In the mill you should set the pulley on the table on a pair of parallels which should cater for the face being true and then pick up the OD with the indicator to get it concentric.

Indicating off the bore is just too small a setting area and you can be out a couple of thou which will make the pulley oscillate and vibrate like nothing on Earth.

Re-saving the pulleys is a matter of cost.......it cost more in time and labour to bore out the pulleys and make a bush...... which you need a lathe for anyway.

To get the bores right in the new pulleys in the mill.....by that I mean without inadvertently boring oversize again......., you need to use the boring head by "walking up" to the size you want.....that means taking the last few thou in a few cuts and measuring with a plug gauge or telescopic gauge and micrometer.

You "could" put a shim in the bore of the pulley (full diam) if it can be re-set up and bored to the size to accept a shim of the right thickness.......this is almost like having a bush without turning one in a lathe......but the sizes must be spot on........bore oversize by .010" to use some .005" thick shim material....(.005"per side)......any old size to plug the gap just won't do.

BTW, investigate whether you can obtain pulleys with a taper lock bush in the middle which makes attaching to the motor and spindle a piece of cake.

The motor and spindle diams should be a standard size, so you need to state them EXACTLY when you go to buy the pulley and taper lock bush.

DO NOT BORE OUT A TAPER LOCK BUSH IF YOU GET ONE THAT IS UNDERSIZE........IT'S AN EXTREMELY DIFFICULT JOB TO DO EVEN FOR THE EXPERTS.
Ian.

[cowanrg]

handlewanker, this is pretty good information. I'm still learning, obviously, and I understand what I did wrong.

I indicated from the center bore, which as roughly 1/2". However, there was nothing on the outside to use, since it's a timing pulley without a flange.

I used a boring head before and slowly increased the bore size until I was close, but I overshot it by forgetting that one tick on the boring head is equal to twice that in diameter. Silly mistake.

I will check into stock pulleys, but unfortunately, the spindle bore is very strange, it's 24.5mm, to the outer splines. I doubt I'll find something off the shelf for that. The motor is a 14mm bore, which is a lot easier. Unfortunately, everything is metric, which is a LOT harder to find.

I think I'm just going to get a lathe (probably just a small HF 7x10 or 7x12) and make some v-belt pulleys instead of redoing the timing pulleys. Thoughts?

[handlewanker]

Hi, I had to go back and re-read what you were trying to do.

The odd sizes (on the spindle) are because you have a splined shaft and the OD of the shaft is not a standard size, hence the 24.5mm size you have.

The motor shaft, being a standard item for pulley attachment either belt or other, would be a standard size.

How do you hold the new pulley(s) onto the splined shaft of the spindle?.....with a side grub screw?....this will cause the pulley to deflect with the pressure especially if the pulley is a loose fit.

Although it is a bit far down the track, I would have fitted Poly Vee pulleys and belts.......they have multiple raised Vees on a flat belt, running along it's length on the inside face, not across it like a timing belt.

The belt is thin and flat and almost as flexible as a plain flat belt that was used on machinery many years ago, (and is still used on the old stuff)

The main attribute is the belt will run smoothly and track accurately even when it is "slightly" out of alignment due to the multiple grooves in the pulleys acting like tracking devices, similar to a single groove conventional Vee belt pulleys, but just a lot more flexible, especially when it has to wrap around small diam pulleys where a regular Vee belt would soon fail.

I would not fit a toothed belt for any drive device that did not require accurate positioning characteristics, and in your case you only want to drive a spindle to rotate a cutter.

Compare your needs to a drilling machine where the motor only has to rotate the spindle to enable the drill to cut......belt tension takes care of the torque needs.

You will still have to ACCURATELY bore any pulley you want to fit to the spindle because as far as I know you have a splined shaft.

Attaching it to the spindle is a different kettle of fish.........that is why I suggested the taper lock for the pulley which has a tapered bush in the middle and allows you to clamp it directly to the spindle ( after boring to size) without the need for side grub screws or keys.

There is really no other way to attach the pulley to the spindle unless you have the new pulley bored and subsequently splined to match the spindle......but it will be a sliding fit on the spindle and again a grub screw is not the answer to holding it firm.....you are going against convention with the mod.

The taper lock bush system acts like a collet and clamps evenly to the diam of whatever you want to attach it to.

You also still have to align the motor shaft to the spindle or you will get problems big time.

BTW, unless you have a real need for a lathe, it would be heaps cheaper to pay someone else to supply you with the pulleys with taper locks to your specifications.......just don't supply the pulleys and get someone to bore them.........one slip up on the boring and it's your money gone.

If the boring turns out to be not accurate, you refuse to pay........there are only 2 pulleys you have to have supplied and bored.....the other 2 can be supplied to the 14mm diam you need for the motor.....$50 - $75 per pulley for the odd diam sizes for the spindle would be extremely cheap.
Ian.

[bjones]

the skyfire cnc mill uses timing pulleys and belt as do some sieg x2 and x3 models, it's a common usage for spindles.
http://i1336.photobucket.com/albums/...psd2a18ef9.jpg

[cowanrg]

This is all really interesting. I see lots of people using timing pulleys, including Hoss. It seems that it's really not the best way to go, and I wish I had known that before I bought them and started this, but I just saw so many other people using them.

I'm switching gears (ha) and going to do v-belt pulleys instead. I understand that the taper lock bushing is better, but it just doesn't seem practical to do in this situation, with 2 speeds, and a strange shaft size, because of the spline.

Yes, I will just bore the pulley to the outer spline diameter and use set screws to secure it to the shaft.

[bjones]

not the best how? while v-belts can be more quiet timing pulleys won't slip so are best for transmitting the power and are good for use with servos for tapping. they are used often because they are very plentiful and cheap and can be made to work without needing a lathe when properly set up as the others have pointed out.if you are wanting an excuse to get a lathe going the multi rib v-belt route will necessitate that.

[cowanrg]

it just seems like it's a pain to get aligned correctly, or at least that's what I was finding. but I think my problems are mostly because I didn't get the bores centered.