Best belt for variable speed lathe conversion? H timing belt? HTD? Poly V?

[mmurray70]

Hi guys, I have a colchester triumph 2000 lathe and im sick of listening to the gear noise in this machine. Im In process of converting it to run variable speed with a VFD and plan on using a belt drive from motor to spindle and bypassing all gears (just setting levers in a neutral position). Im debating on what type of belt to use and looking for advice...

First choice is H series timing belts. I would use 1.5" wide belts and a 9.5" diameter pulley on spindle. These are readily available in size I need from mcmaster and reasonable price. Downside is the H profile isnt really perfect for power transmission. Leaning towards this option because belts/pulleys are easy to get. Do you guys think this would be able to handle the power from a 5hp motor?

Second choice is 8mm HTD timing belts. This profile has more teeth and is better for transferring torque. But it comes in odd sizes. 30mm width is nice bit smaller then 1.5" (losing much of the advantages) and next size up is 50mm which is hard for me to fit. Also big pulleys are not available from mcmaster and they are at least double in price of comparable size H series pulleys. Could make the big one I guess but its a lot of extra work.

Third choice is Poly V belts. These would run smoother and quieter then any other belt. I think this might be whats used on newer colchester VS lathes. But im not sure if would handle the torque? Come to think of it thats what is used on my fadal mill and they use these belts up to 15hp. Maybe i should give this option a closer look? Pulleys would be easy to make if not available.

Any suggestions?

 

[TGTool]

I vote for Poly-V. There should be one for the horsepower requirement and it would minimize any vibration that cog belts might introduce.

 

[rklopp]

My Chipmaster uses timing belts in the high speed range. They sing or buzz due to the teeth, so are not particularly quiet. I vote for poly-V, too.

 

[gbent]

What ratio are you planning to use between your motor and spindle? If you have a 1800 rpm motor and belt it 2:1, you will have a 900 rpm spindle. Roughly speaking, a vfd is a constant torque device, so at 1/10 speed you will have the same full torque, or 1/10 the horsepower.

There is a reason most CNC machines with variable speed motors still had a gear box for high/low.

 

[GregSY]

V belts are still king.

But you're nuts to do what you're doing....gears are there for a reason. Relying on a VFD is buying a battery powered push lawnmower to mow 5 acres of land. Yes, it will do it in theory, but in practice it's gonna suck. A set of earmuffs is about $30 and will solve your sickness issue.

 

[beckerkumm]

Have chased down why the gears are noisy? Is it every speed or just some? Have you looked at the gears for damage or loose set screws? Generally you need several gear choices or double the motor size to get close to the hp and torque range with a vfd you have now. Been there, done that. Dave

 

[dgfoster]

Polyvee belts can easily provide the needed power and are durable and quiet. A good number of people have converted their Monarch EE drives to VFD/belt drives. But, I think they also retained the back gear. I would suggest you look in that forum to learn the caveats. I agree that the VFD will be able to run the lathe over a wide range of RPMs, but using some gearing can improve its power performance over that RPM range. I run a VFD on my mill and love it. But not having back gear would be a major loss. And sometimes I even change the belt on the step drive if I am running a long job that benefits from allowing the motor to run at optimal RPM for power production.

Denis

 

[mmurray70]

Ok I think im going to go with poly v belts. Fadal actually used these up to 20HP. Automotive applications use them to drive superchargers and everything! Should be fine. Anybody know a source to buy these premade or am i stuck making my own? Im thinking 10 rib PK profile. about 1-3/8 wide.

For you guys doubting the project I have an awesome plan for this machine! Been wanting to do this conversion for years but it has a belt driven oil pump for the head lube and this was holding me back as variable speed wont run the oil pump properly. And I was also concerned with lack of torque on some jobs. But I have solution to both problems. I plan on leaving stock motor in place, with pulley and all there, so it still drives oil pump. Im leaving everything in place for the stock drive train, and just removing the stock drive belts. Im adding a second motor to the rear of the machine driven by VFD. This will be run with single belt reduction to spindle. And im sure this will be plenty of torque for my needs 99% of the time. I do use this machine to drive some large taps occasionally and if I ever need the extra torque ill just pop off the timing belt and install the stock V belts and take advantage of the gears.

This is general forum so maybe some of you guys are more familiar with manual machines but most CNC lathes these days are belt driven with a single ratio and have plenty of torque. I was originally planning on using a 60t and 14t timing belt setup so this gives me a base speed of 400 RPM. I should be able to overspeed the motor at least 2.5 times to get 1000 rpm top speed which is all i really need. And with 7.5hp motor (sorry i said 5hp in origional post) I should have around 100ft lb of torque which should be plenty for nearly all my work. If I need more, 10 mins to change belts Best of both worlds. Cant wait to get this done!

 

[gbent]

Ok, so you have a plan for when you need more torque so you should be good. Yes, I agree with your statement about most CNC lathes these days. But you are glossing over the fact the machines are designed from day one for vfd, including encoder feedback. They also have independent ventilation to ensure cooling.

You may be able to find automotive or truck sheaves that will work for your project.

 

[lucky7]

I have the same kind of lathe as OP. It can easily cut 1/2” diameter aluminum parts as well as 18” toolsteel discs in the gap. No vfd single pully set up will allow such a wide speed and torque range. Glad to hear the OP is keeping the headstock gearbox.

 

[AlfaGTA]

CNC lathes get away with single range drives because they have real encoder closed loop feed back and a real spindle drive that compensates for load on the spindle...
I own a Romi M17 CNC (10 hp) lathe that has a single range spindle drive and it is not good for any large diameter work...Needs more power to the spindle.
Romi added a 2 speed gearbox to their next larger CNC lathe to get the needed torque for large work....
Single range drive requires lots of smaller depth cuts to work larger OD parts...Not a real problem on the CNC...But on a manual machine you are going to hate it!
Closest thing on a manual machine is the Monarch EE. That was designed for relatively light work, and even there they have a two speed gearbox to get the needed torque.

Cheers Ross

 

[GregSY]

Oh wait...you said poly V belts. No, they are sucky. A regular olds style V belt is better.

Poly belts arose when auto makers needed to drive multiple loads one one crank and had limited space to do it. People think poly belts are sexy as a result and it becomes a given that poly belts are best for everything. They're not. For an industrial piece of machinery, like a lathe, a V belt is way better and easier to implement.

 

[AlfaGTA]

I disagree!, Polly "V" works fine for industrial drives. Lots of CNC lathes use them for the spindle ...Both my Romi and Deckel FP4NC use them for the main motor.
drive.
Just have to engineer the belt size to your power requirements....
They run cooler and with less noise than "V" belts also impart less mechanical "noise" to the rotating part ...Can handle larger size differences (smaller pulleys if needed) than "V" belts...Use single pulleys at drive and driven ends where V belts often require multi pulleys and matched belt sets to handle the power.
V belts are cheaper, and easily obtained ....That is their big appeal....
Cheers Ross