What pulleys to use for a milling machine and VFD.

Evening, I'm upgrading the pulleys and belt on my milling machine to something better. It currently has a very thin belt on there. Currently the speeds are: 1000, 2000, 4000 or 6000 rpm so I'll change (maybe) 1:2 ratio pulleys and use a VFD.

Should I use pulleys and belt with teeth or V profile?

And where to get them?

The belt only drives the vertical spindle, not the table drive.

I would be inclined to use a Poly-V (multi-rib) belt.

Martin.

The four ratios use the motor running at the nameplate speed Giving the maximum available motor power.

By using one only gearing ratio of 1:2 and using the VFD for varying the motor speed means at low speeds the power drops off as the speed is lowered. Unfortunately this is just what is not wanted.... Bigger cutters require lower speeds and more power as the diameter increases.

I have a project in mind that requires a spindle power of 5 HP, about 3 KW. It would make life a lot easier to use a single pulley drive and allow the vide to do variable speed The project is a Vertical mill. a speed rang of 40 to 5000 rpm would be nice!

Has anyone in the forum already done this?

Regards
John

Hi Chris,

As Martin says, Poly-V belts is a good solution, if you want a belt with teeth/ timing belt you get a belt system that is compact and can transfer a lot of power. A belt system that lowers the speed compared to what you have now will give you more torque when running a larger dia. cutter. To find a supplier just google for timing belts (or Poly-v if you go that route).

Thor

Agree with John about the limitations of speed / power combinations using a VFD controlled motor with only a single speed drive. Probably best to have a two speed belt set-up with decent overlap in the middle ranges.

My previous mill was a Chester Lux style, R8 taper, machine with two speed belt drive and VFD controlled 2 HP (?) motor. Don't recall exact speeds but performance was very satisfactory with low range from 125 to 1400 and high range from 250 to 2,800 rpm. I imagine the belt drive ratios were 1.5 to 1 up and down relative to nominal reduction. The considerable overlap in speed ranges was very useful as belt shifting on that machine was something of a faff so it was nice to be able to set-up for slow, larger cutter, jobs and fast, smaller cutter jobs.

I imagine that something like 3 to 1 variation between high and low belt speeds would work better for you as your machine is clearly much more high speed capable than mine was. Not that happy at 2,800 rpm so higher speed range would have been wasted. The extra drive in low range with larger cutters was very noticeable tho'. Although high range would turn larger cutters just fine there was no chance of really exploiting any that needed to be driven below around 600 rpm.

Clive

Ok, thanks.

It's not the biggest mill, but it is high speed as it is designed for drilling as well.

What sort of range does a VFD give you? And should you have the pulleys turn the spindle at the lowest speed you will use so you don't lose torque?

It I might even be worth changing to a 1hp motor that runs at 1400 rpm instead?

Theoretically VFD speed range goes from a few RPM to around double the motor nominal speed. In practice power at very low speeds is tiny and going too high risks mechanical damage to the motor. The general run of affordable VFDs are pretty much constant current devices so motor torque will be fairly constant hence very little power at very low speeds. The more sophisticated, and more expensive, VFD boxes are able to considerably boost torque at lower speeds when correctly set up but significant gains, and they can be very significant, comes at considerable extra expense and a much larger instruction book. VFD instruction manuals are not in general known for clarity to the uninitiated user!

As a very general rule of thumb speed variation of around ± 1/3 rd of the nominal speed with pretty much any motor and any machine tool application is effectively invisible to the user. Most modern VFD boxes have some degree of torque boost in the - side of this range so although power will be reduced at lower speeds its not exactly pro rata. But we rarely run our machines at anything approaching rated power anyway. Usually ± 1/2 nominal speed will be satisfactory but ideally one should check how much oomph you will need. An extra fan is probably a good idea if planning long runs below - 1/3 rd nominal speed. Motor fan efficiencies drop off considerably at lower speeds but near constant current drive means that pretty much the same amount of heat is going into the motor.

Experts can safely get a much wider speed range but we ordinary folk had best be conservative. Vector drives do better than basic ones and, in general are kinder to the motor. Probably worth the extra cost for a mid range vector unit rather than bargains.

Clive

Edited By Clive Foster on 17/07/2014 21:38:27

Edited By Clive Foster on 17/07/2014 21:39:11

Hi All

I have been thinking on a build it yourself spindle belt transmission and VFD motor drive for a while,....
to be used in a Epoxy frame CNC Mill. .

The following links have been very useful

For the belt transmission I like the following mechanism as used by Fadal a US company, now mothballed in new hands. They made a range of CNC machines, some of them used a novel drive system employing Polly V belts. The belts were constrained within a containment that kept them clear of the pulleys except when an idler wheel was pressed against the back It sounds complicated but would be fairly simple to make.. This mechanism allowed the belts to be alternately switched in and out allowing the speed ratio to be changed automatically by the CNC system, although it could be done manually if you do not want to mechanise it.

(Oh.... and yes in recognition of the Myford Mavens The tri lever system was similar but not the same) Fadal did it rather well!.....Sorry I could not resist......I Ducks for cover!

Item 14 in the following thread is of note:"

Quote: "I have a Fadal VMC 15 with a 10,000 rpm spindle. This has a 2 speed, 8 rib poly belt drive system. This was a factory build option, same parts as the larger machines. Nice and quiet , same belts for 10 years. I think the drive ratios are 2-1 for 10-2500 rpm and 1-2 for 2501-10,000 rpm. The torque is good in low range aprox. 250 ft lbs and it will push a 1.500 drill no problem. The milling performance is limited by chatter on larger tools and deeper cuts. The VMC 15 is not a heavy duty machine.

**LINK**

From this general Google search:
**LINK**

The following Blog is definitely worth studying also:

It covers in an easy to understand way some of the issues involved in designing a spindle and drive system very well. Get a cup of coffee first you will be reading for a while,
**LINK**

From the blog a link to parts manuals that show the device.
Get a set of manuals for the 4020 machine
The links worked for me.
**LINK**

Regards
John

Would this motor be suitable do you think?

http://www.ebay.co.uk/itm/3-Phase-Electric-Motor-1HP-0-75kw-1400rpm-80-frame-/110912538780

My Jaguar Cub comes with automatic torque boost pre-programmed. There are a number of options for twiddling this which I have left alone, but my impression is that there is adequate torque even at low speeds with a 2:1 reduction compared to motor speed.

Neil

Chris

I've not looked at the link you gave but its a motor so it might be OK. So much depends on what you are trying to do.

From your description your machine sounds quite small so 1HP seems a lot. (it wont give 1HP with the circuit you posted earlier though) Since you started asking about three phase motors running on single phase I assumed you already had the motor. If you don't have three phase supply then by far the best option is to use a VFD.

Please don't be put off by the warnings of motor damage or lack of torque at low speed etc, whilst both are true I have never heard of anyone actually damaging a motor and the reduced torque at low speed can be a positive boon. I use a VFD on my Fobco drill and have never moved the belts since I fitted it. At low speed (less than 50RPM) I can drill stainless up to 2.5mm diameter and keep the drill cutting with lots of pressure, but the main bonus is when tapping. For small (less than M2) I limit the torque by not overtightening the chuck, but above that size the motor stalls and I can back out as the VFD reverses easily.

On my milling machine I have set the VFD so that the motor only just creeps as the lowest setting. Its ideal for edgefinding or setting up with a DTI sweeping the job.

I would suggest you definitely keeps some belt changing options but use them with a variable speed motor. so you still get a full low speed torque if you are using large cutters etc.

I have three VFD driven motors, non of them have special motors made for variable speed use but all have no problems running them between 18 and 150Hz (one runs at 12Hz) so very wide speed ranges are not difficult to obtain.

I am sure if you gave a little more information about your setup you would get lots of good advice here.

Ian P

Interesting, thanks.

It's an Aceira F3, the main motor is 3hp which drives the table and horizontal head. The standard milling head is missing and I only have the high speed head which is 1000, 2000, 4000 or 6000rpm. The problem is that the drive belt is only a few mm thick and slips under load. Everything else seems fine, it's just the tiny belt and pulleys that let it down. This motor is 0.5hp, but it is built into the casting on top of the mill and there isn't much room to put bigger pulleys etc on, certainly no room for more than one pulley. So the idea is to build a new motor / pulley setup on top of this head.

Im img currently working through the links a few posts up!

Chris

An F3, now I'm envious!

I dont know the head/motor construction details but all else being equal, a three phase motor is smaller than a single phase of the same power. If you uses a VFD and modify the (I assume) current 4 step pulleys to give two ratios you should be able to get Polyvee to fit in the same space. Polyvee can transmit quite high power through small pulleys and at close centres. Another big advantage is they are very smooth and should be vibration free.

Things like surface and toolpost grinders often use flat belts to get the best surface finish, Polyvee come a very close second and would be ideal on a high speed miller.

Ian

For motorizing the Aciera high speed head I would use one of the brushless DC motors, which are sold by Sieg. They include the control box also. I don't know the prices, but regarding the prices of the machines which use them they cannot be very high.

Regards, HansR.

Chris, if you can't replace the .5hp motor, you could strip it, remove the armature and shaft, replace the shaft with a longer one the sticks out the top end of the motor casing, put a pulley on, and mount the replacement motor parallel to the original one. Just an idea. Ian S C

I have added a Polyvee drive to the Dore Westbury milling head on my Tom Senior M1 milling machine. It has three belt pulleys but I rarely use the other pulleys just the mid range and an inverter control to the half HP motor. This works very well. I Was going to add a couple of photos in my photos section, but I cannot not see how to do it. Has something changed? Found it under "Albums," Who would have thought it?

Alan

Edited By Alan Jackson on 07/08/2014 10:42:06

Edited By Alan Jackson on 07/08/2014 10:53:29

Looks good!

I'm not entirely sure what you mean Ian? What would be the purpose?

Chris

Which Ian?

Ian P

Ian S C.

I'm looking into your polyvee idea though.

I was just thinking(bad)if a motor could not be replaced because it was part of the machine, this could be a way to overcome the problem. Ian S C