[cnc-newb]

i see belt drive conversions for the x series of mills and most seem to use v-belts. why is this? i was under the impression that a toothed belt system was more efficient over a v-belt. since the x mills have variable speed motors, i would think the toothed belts would be basically "free" power over a v-belt.

please let me know - confused

thanks

[LeeWay]

I think it may be just a cost issue. Like ball screws compared to acme screws. Both work. One is more efficient, but comes at a higher cost.

[philbur]

Why do you say that a toothed belt is more efficient than a V belt? Providing your V belt isn't slipping, which it shouldn't be, I doubt there is anything in it.

A tooth belt is normally used when you want to maintain "timing" with some other part of the machine.

Phil

i see belt drive conversions for the x series of mills and most seem to use v-belts. why is this? i was under the impression that a toothed belt system was more efficient over a v-belt. since the x mills have variable speed motors, i would think the toothed belts would be basically "free" power over a v-belt.

please let me know - confused

thanks

[philbur]

Because V belt systems drive on friction the belt needs contact angle in order to transmit power without slipping. This limits the maximum ratio and the minimum pulley diameter for a give power transmission requirement. Tooth belts may be able to transmit more power for a given physical size.

Phil

[LeeWay]

I have noticed that with the belt drive conversion from Steele, I do get a little slippage in high speed. I need to quantify that though. This is with a different motor with much higher torque than the OEM X2 motor. The X2 motor would have stalled long before this slip point on this vbelt.
It slips some when adjusted correctly because on these two pulleys, the sizes are close to the same size. This doesn't let the vbelt wrap around the pulley far enough to prevent the slip.

I am going to turn the smallest pulley off the motor side and lower the motor to be inline with the larger pulley on the spindle. Hopefully this will give me more torque. I know it should give me more speed.

If this doesn't do what I want, I will use a timing belt. They surely won't slip.

I have a serpintine belt on my truck. It is a multi groove belt. I think it is a lot more forgiving of pulley size and can carry more torque than a standard vbelt.
They have much more surface contact to spread the friction on.

A timing belt is more like a chain and sprocket. It doesn't use friction, but teeth instead.

[LeeWay]

Why do you say that a toothed belt is more efficient than a V belt? Providing your V belt isn't slipping, which it shouldn't be, I doubt there is anything in it.

Phil

Vbelts need to be tighter and put more pressure on the pulleys and bearings. They can a sometimes do slip some. We have all seen it. On a high speed start up or when the pulleys encounter torque.
I an no engineer, so I can't quote any formulas for efficiency between the belt types, but a toothed belt that needs less pressure on the belt to work and has no chance of slipping, seems to me to be more efficient than a vbelt.

[philbur]

Yet but a slipping V belt is a gentle reminder to ease up a bit. With a toothed belt it just eats itself if you over load it, V belts are much more forgiving when abused.

More or less efficient depends as much on your ability to design th system correctly as it does on the system you use.

Phil

PS: A good engineer is somebody who can do for a penny what any fool can do for a pound (GB pound that is).

Vbelts need to be tighter and put more pressure on the pulleys and bearings. They can a sometimes do slip some. We have all seen it. On a high speed start up or when the pulleys encounter torque.
I an no engineer, so I can't quote any formulas for efficiency between the belt types, but a toothed belt that needs less pressure on the belt to work and has no chance of slipping, seems to me to be more efficient than a vbelt.

[cnc-newb]

i am just basing my question off of the years i use to work at a machine/performance shop. take superchargers - the smaller ones likes paxtons (not sure what else is a smaller supercharger, been out of it for a long time) and the like would use serpentine belts at most, but the larger 6-14/71s would use a form of a toothed belt due to the amount of power they need and also their efficiency. i just downscaled the items but thought the same principles would apply - less wear and tear on the rotating parts and more power going to the cutter due to less friction in the transmission of the power

[philbur]

It is true that V belts use friction to transmit power but providing there is no slippage there is no frictional losses. The use of a tooth belt on a supercharger may be more to do with the compactness of the design rather than any efficiency considerations.

V belts drive systems are used the world over in machine tools with much higher power requirements than a small bench top mill.

Phil

i am just basing my question off of the years i use to work at a machine/performance shop. take superchargers - the smaller ones likes paxtons (not sure what else is a smaller supercharger, been out of it for a long time) and the like would use serpentine belts at most, but the larger 6-14/71s would use a form of a toothed belt due to the amount of power they need and also their efficiency. i just downscaled the items but thought the same principles would apply - less wear and tear on the rotating parts and more power going to the cutter due to less friction in the transmission of the power

[cnc-newb]

to be honest i can't remember the numbers but even when people would put a toothed belt setup, at least on cars, for smaller items like alternator, a/c and steering there was less of a hp rob than the vbelts. if i remember correct, the order of efficiency went toothed, serpentine and then vbelt. i will look for #s to back up what i am saying. and these were dyno proven, but i guess in the scheme of things, the amount wasn't high in the %s as these were high hp street engines - 500-700HP on average.

i just figured that since we were dealing w/ much smaller units of power any additional benefits would be exponentially better.

[LeeWay]

Most of the higher HP v belt setups use multiple belts as well. Matched belts too. These are costly, but very effective at spreading the friction needed to drive a load. Even matched v belt sets for big machinery are probably a lot cheaper than the same size in a timing belt or multi v belt.

It still all comes down to design, cost and effectiveness or put altogether, efficiency.

The L belts in the Steele belt conversion are really small, but they are fully suitable for the duty it was designed for on an X2 head. I increased the available torque with another motor and then the design starts to show it's weakness. If the belts were designed correctly with the right sized pulleys for this larger motor, I should be able to stall the motor before the belt slips. That is the case with the original motor and design.
To get the torque I have available, I will have to modify or redesign. Since there is very limited space atop the X2 head, a timing belt would likely give me the best performance and the least amount of slippage.
Here is an image of my motor setup with the Steele belt drive. You can see there isn't much space to work with there.

[Oldboy]

Hay LeeWay
How about giving us all the details on that motor mod.
Like where did you get it?
AWSOME!

[LeeWay]

Here is the link to my build log.

http://www.cnczone.com/forums/showth...t=32609&page=2

I got the motor from Ebay here.

http://cgi.ebay.com/Diamond-Back-Tre...QQcmdZViewItem

The best drive came from here.

http://www.surpluscenter.com/item.as...tname=electric

I did get the heatsink as well. It is running off of 220 VAC. This motor has plenty of torque.

[Glennza]

I think one of the big considerations is cost. Let's face it, we can all be pretty cheap at times and v-belts are cheap. And with a little bit of work we can make the pulleys.

Of course, we could also make the timing pulleys, but that's about like cutting a gear, so why not go all out and make a gear train? Great, another project that I'll over think and never complete!

All kidding aside, V-belts are inexpensive, the pulleys are easily fabricated and millions of machines prove that they work.

Glenn

[blades]

I think that the timing belt is truly more "efficient" in terms of friction, but that negligable efficiency is of no consequence on our X2 mills. I do like the safety feature of a V belt setup, almost like a clutch. BUT, that can be a bad thing, especially in the case of a CNC converted machine. The spindle belt may slip, but the table is going to keep moving! What really appeals to me about a timing belt setup is the fact that you're able to take a substantial amount of axial load off both the motor and spindle bearings.... preload that is otherwise necessary with a V belt setup. Timing pulleys and belts are really not that costly, and the timing pulleys tend to come in configurations that are a bit closer to what we want to work with to retrofit to the mill. I haven't seen any readily-available small V pulleys that are nicely machined like timing pulleys. Since I don't have access to a lathe, I'm thinking a timing belt conversion will be one of my upcoming projects.

[rabidgoalie]

It may be that with a V style of belt, you have a built in point of failure...and the only consequence, in this case, is that you will have belt slippage. With the OEM set-up, you have nylon gears that were probably designed to be the point of failure in the drive train of the machine.

If you were designing the mill, and you knew that at some point you were going to have a load on the spindle and something was going to break you would rather it be the cheap nylon gears rather than the drive motor or the spindle and/or spindle bearings. This is a fairly common practice. On the DeWalt DW735 planer, the main drive pulley connected to the cutter head is made of Zamax and is the part that always breaks. People complain about this constantly and call it a design flaw. They wouldn't if they saw what could have happened if that pulley wasn't the built-in point of failure. 13" razors attached to a cylinder flying through the air isn't a pretty thing I am sure.

So, perhaps when the designers of these belt and pulley conversion kits sat down to design these they took that into consideration. If you remove the designed point of failure something else becomes the new one.

[LeeWay]

Yes, but timing belts are still the point of failure, just a little higher point to shear the teeth.

[philbur]

Either system can work well if designed correctly. Designing by guess work or "because it looks right" can mean a lot of wasted effort regardless of which system you pick.

There's a lot of info out there on how to design belt drive systems. I recommend that any would-be designers read and understand it.

Phil

[MIKE JEFFERS]

my belt conversion uses a timing belt and toothed pulleys
but thats because it's what was to hand

[blades]

my belt conversion uses a timing belt and toothed pulleys
but thats because it's what was to hand

Mike, do you have a pic of your timing belt conversion?