Belt Squeal - Belt Dressing

[awemawson]

Has anyone experience of the drive belt sprays that are supposed to stop belt squeal? Reason for the question - I have a multi-vee belt (a big 'un ) that takes power from the 25 hp main spindle motor of my Traub CNC lathe to the spindle. Now this drive can accelerate at a great rate of knots when the speed changes resulting in a squeal. I was confident I'd find that the belt was slack but when  I took the covers off this morning it was as tight as anything - in fact possibly tighter than I'd have adjusted it myself feeling the slight deflection.

Just maybe it needs changing but it looks ok hence the question about the various dressing sprays that are around - has anyone any experience of them?

[mattinker]

My personal experience of belt squeal has been from belts bottoming, worn pulleys allow the belt to run on the flat between the "V" thus reducing surface contact and eliminating or reducing the pinch effect of the belts running in the "V".  Turning the flat of the bottom of the "V" is a possible solution, new belts don't usually solve the problem!

The belt grip sprays I've seen are for flat belt applications.

Hope helps, regards, Matthew

[awemawson]

Interesting thought about bottoming out. I don't think so in this case as it's 'multi vee' but I will put some marking blue on the flats of the pulleys and see what gets polished off.

[mattinker]

If it's bottoming out to an extent where it squeals, the flats are usually polished. If some of the belts bottom, that would throw the load onto the other belts, making them slip.

Regards, Matthew

[Jonny]

Matts definitely right I had motor spin with a dual pulley and belts on my old scrapped 140.
Tension made no difference neither did a new belt, V was running in to the bottom flat, pulley worn away.
Short term fix to get me out of the proverbial I did have to use that belt spray daily and take pissy cuts.

[Pete.]

We have large diesel-powered road saws that wear the pulleys too. They have a set of 10 vee belts driving the cutting blade  and they slip like crazy when they bottom out.

[awemawson]

I should perhaps have stressed that this is a 'poly vee' belt ie 5 (I think) Vees all as one physical belt. Tonight I've examined the pulleys and the belt very closely - on the pulleys although the sides of the Vees are polished neither the crests nor the valley bottoms are polished. The belt crests are dull as well. So I marked with a Dykem pen every two inches across the crests of the belt on the assumption that it would quickly be spun off if the belt crest were bottoming. I then went through several fast acceleration cycles to see the result. Guess what - not a squeal to be heard  oh and the Dykem was still on the crests !!!!

Conclusions to be drawn - none 

Andrew

[angus]

have you checked the alignment ???
last one of those that was protesting at work, one of the pulleys was trying to slide off the shaft... was over 1/4" out over about 3 '

[lordedmond]

Andrew

put a bit of talc on the belt that will help



got the tip from a Merc mechanic when I took our new ( heap ) 190e in because of the squeal

BTW that car was a complete heap left us stuck in Scotland when it was six weeks old and then when downhill from there


Stuart

[awemawson]

ho hum .... the plot thickens. Took off the covers again this morning to try and check the alignment - impossible  The motor pulley has a bit of flange that a long ruler can be laid on - but the pulley on the main spindle has virtually nothing protruding. Laying my 24" ruler along the motor pulley flange it's short by 6" - trying to do the same with my 1 metre rule theres no way it's going in   

So when all else fails read the manual : I found a paragraph in the maintenance booklet referring to belt tension, and just maybe I've underestimated how much tension is required on this belt. They refer to a 200 Newton force depressing the belt half way along and getting 14 mm of deflection. Now 200 Newtons is far more force than I've been exerting to get about 1/2" of deflection. So just perhaps it only needs tightening - that seems an awful lot of side force on the spindle bearings   

I certainly hope that the belt doesn't need changing in the future. The spindle has the  drive pulley, then the belt drive for the rotary encoder, then the spindle hydraulic brake, then the hollow hydraulic cylinder for the collet closer all mounted on the end all with their associated pipes and wires - it would be a long job !


... but at the moment it's not squealing !!!!

Andrew

[PekkaNF]

Hmm. 200N (aprox. 20 kg equvalent) does not sound a awfull much of load to any decent size bearing. Most roller bearings needs some minimum load or they will wear out no time.

Can you compare side of the tensioned belt to side of the pulleys? Like two long linears and gauge blocks (key stock)? This was the way I checked my brother auxiliary belt on his car. Asked him to hold one rule against the belt and placed another rule on the cam shaft pulley....error was very visible then.

PekkaNF

[awemawson]

  yes I'm out by a factor of ten 

I was thinking 200 kgs !

Andrew