spindle belt don't last

[samu]

Machine:hardinge VMC1000
Problem:Spindle belt become noisy after only a couple of hour(less than 100).
i check tension but the two belt has not exactly the same tension. Belt has a sticky yellow dust on the bottom. They run hot enough and one of them has some deformation on one side. Last belt has many little crack after only 500 hour.Aligment between sheave seems to be ok. Belt run smooth in M04 but noisy in M03. It is worst when belt are cold. I use cimtech 304MA coolant wich let a sticky deposit. I suspect that it could be the cause. Belt stick on the pulley and make noise when it unstick. That cause excessive heat and premature faillure. Any hypothesis are welcome. This noise make me crazzy!

[machintek]

Because you have 2 small belts, I think you have a high speed spindle. Not the "normal" 4K or 6K. Am I correct on this?

George

[samu]

8k spindle

[wildwestpat]

Hi Samu

There are differences between belts from different manufacturers. The belts are driving relatively small radius pulleys and this can cause the belt to swell and pinch on the sides. The cracking is indicative of this but should run for some considerable time before snapping or sheding lumps of the case.

You mention the coolant geting on the belts and this is not good. Clean the pulleys and degrease them fit new belts of the type designed for high speed use on small diameter pulleys and the problem should go away.

Regards - Pat

[MrWild]

You need to replace belts in matched pairs. Unmatched belts fight each other and wear fast.

[machintek]

There is another consideration. The spindle motor is bolted to a piece of plastic. This as heat insulation. but putting a lot of pressure on this plastic while tightening the belts causes the motor to tilt a bit because the plastic is bending. This causes one of the belts to have less tension. I do not think Bridgeport has changed this design. But look into it. I suggested a long time ago a sandwich of metal and silicone glass (G3, melamine) to prevent motor heat from getting to the head.

George

[samu]

I use GATES polyflex JB belts wich are designed to run at high speed on smal pulley.So i don't think it is the belt itself that cause the problem. But, effectively i never ask for matched pair. There is a number on the belt apart of the identification number. It contain one digit and two letter. On evry pair of belt that I fit, this number was the same but different from one pair to another. Does it mean that it was matched pair???.

[jbo]

Hi Smau

I have two of these machines and undestand what you are going through.
We replaced the belts with one belt but had it split therfore ensuring it was the same length.
This helped a lot.We have found that the tension is critical to quiet operation.
After changing the belts we retension them again after a couple of weeks of service and they stay fairly quiet.My service guy has a proper tension gauge and the use of this made a big difference.
I hope this helps in some way
Regards JBO

[samu]

The realy strange thing is that it run very smooth in M04 but not in M03. Does anybody has an explanation for that.
Maybe should i buy left cut tool

[Nawrocki4Life]

Hello Im a service tech that works for a company that used to rep Hardinge out of Chicago before they dropped us, and many others in Feb....

Any hoo, Your machine uses 850mm belts I believe. Though for some reason Hardinge changed the design to 900mm belts as well. To be honest though, either would work for the fact that there are holes on the spindle motor plate for either. I usually go with the 850's though.

When ever I have changed the spindle, motor, or just a pulley..... to work correctly, they need to be balanced in the machine where it sits.

The way the system works is.... either a direct 1 to 1 motor pulley to spindle pulley or a hi/low gear box which the motor is inputed into a gearbox then that gearbox has a output shaft with a pulley on it belted to the spindle..... which is really the same set up to the belts.

Diffrent RPM machines use the same style belts but their length change due to diffrent size pulleys.

Has the spindle ever been changed on your machine or its motor?

At least 1 of the 2 pullies need to have a ring that is in the middle of it to seperate the belts. Usually on motor end pulley on that model.

Coolant on the belts isnt the best situation, but there is alot of machines out there (that ive seen that has that going on.) A filter mist system never hurts in that case though. I would guess that a belt soaked in coolant would last at least 6 months.

Heat from the belts is normal. Now as to "how hot" i couldnt answer that one. When I install a new set of belts, I warm up the spindle for about 15mins ( a spindle warm up cycle). Then I run the spindle at 3,500 RPM for 30-45mins. After that I go back up and adjust the belt tension. Before I do that though, when I orginally install the belts, I set the tension a tad bit tighter then needed. The whole idea of this is because of how that driven system is set up, the belts tend to streach out a bit. If you were using a poper belt tension meter you would be looking for about 85 hrtz on the belts when adjusted properly.

I may be anal or out of my mind by doing that, but I havent had any complaints on the job I did.

Now as to whats going on with your machine. Couple of things to check or think of....

1.) Have you ever felt/spun the spindle without the belts connected? How does it feel/sound?
2.) Have you ever felt/spun the motor without the belts connected? How does it sound/feel?
3.) How hard are you pushing the spindle. Load meter, sound of cuts, ever stall/crash the spindle?
4.) Properly cleaned both pullies before changing the belts?

It also depends on how the belts were stored. Usually they are folded a bit because of shipping or what have you. If the belts are not round when installed and kinda have a "hump" when installed, you need to try and install both belts and have them oriented to where the deformitaty is on each one.

They way I look at it is. Heat on belts is normal, not on spindle nose/tool. If spindle sounds and feels good with no heat on it. No problems there then. If hot...... Bearings, balance of spindle, and drawbar clamping force can effect that. If proper belts are used and the tension on them, cant go wrong there. If motor sounds and feels good, shouldnt be a problem there.

Direction of rotation shouldnt change the way the belts are. I would think it would be more of a bearing noise/drive problem for that one.

I dont know though, this all might sound crazy.... hope any of this can help you though.

[samu]

Originally Posted by Nawrocki4Life I may be anal.

Regardless if you are anal or not here is some point i already checked:

-Spindle stay cold.
-Spindle motor run extremly smooth without the belt.
-spindle rotate freely when i remove belt and i heard no suspect noise when rotated by hand.
-spindle bearing has been changed 3 years ago.
-loadmeter is about 11% when i run 8k rpm in the air.
-load meter have some peak at 120% for short time when making chips
-i don't see anything like a ring that is in the middle of the pulley to seperate the belts.
-the only tool i have to check tension is a kind of "pencil scale" that indicate force and deflexion but there is not enough room to use it in the midle of the belt.

Thank you for your very elaborate reply.

[samu]

Probably not a good thing for the belt, but excelent for my mental health: i spray some WD-40 and the noise goes away. I need to spray again after 1 or 2 day. It seems to confirm coolant theory that makes the belt sticky.