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J Tiers
07-22-2009, 01:01 AM
I have yet to make actual torque measurements (static torque, anyway) but I recently got interested in improving the torque available through the 1" wide canvas/rubber composition flat belt on the Logan.

Evan's negative rake cermet got me going...... I don't get the torque required for that, although my rubber composition belt should be as good as his serpentine.

I see a few issues not directly related to tension*, but tension is the question of the day.

Is there a "deflection" measurement that applies to short length flat belting?

With a v-belt, the typical is 0.5" to 1" deflection depending on the length of the belt. That would be the "thumb pressure in mid span" test. But most long flat belt is run on its own weight tension, like tractor PTO belts, leather ones run to a sheller or a shake saw etc.

I have not seen an objective test for a short span, something like 12" on centers, as typical for a countershaft on S-B or Logan. And nothing for composition as opposed to leather.

Anyone have a typical deflection figure?

I'm figuring I should get about 33 ft-lb per inch of belt width, minimum, and probably more for composition as opposed to leather. That would give the full 1 HP at 1000 FPM belt speed that is typically quoted.

* Oil getting on the pulleys and belt, pulleys rough, where I typically see best results with polished pulleys..... although rougher might work better if there is oil.

Evan
07-22-2009, 02:04 AM
I use asphalt belt conditioner. It's the one type that really works. You need to take a little time to work up the belt to a good traction condition regardless of what sort of belt it is. You apply some of the dressing and then run it unloaded to allow the solvent to evaporate. Repeat a few more times to lay on a coating that is reasonably opaque. Then let it stand for an hour or so to dy out the tar. This gives a coating that only becomes really tacky when the belt slips and heats it up. It is self regulating.

JCHannum
07-22-2009, 08:46 AM
South Bend HTRAL recommends about 1" deflection between the pulleys. Their typical setup is a bit longer than the Logan, so a bit tighter for the Logan might be better.

It also states; the belt "must be stretched tight enough to feel alive when tapped with finger tips." This sounds Zen like, but makes sense when you think about it.

I am opposed to any type of belt dressing. A good clean belt and pulleys will transmit the power they were designed for.

J Tiers
07-22-2009, 09:44 AM
yeah, belt dressing should be an 'adder" not a necessity..... or so I have always been told.

I'm focusing on the two issues of rougher pulleys* and tramp oil now, as tension is "reasonable".

The really polished pulleys, when clean, are exceptionally 'grabby", transmitting much more torque than rougher ones. The downside is that if they get any oil on them, they let go faster than a rougher pulley.

Static torque measurements should tell the story.

Evan: Do you notice any effect of 'tramp oil" on your belts with the asphalt-based dressing? I would think that any oil would tend to decrease torque, and also be very hard to clean off.


* Rougher pulleys are not really rough, but are not polished, they in some cases have a finish that is likely the result of some years useage wearing down a not terribly smooth turned surface. Definitely not the almost mirror finish of many well-used pulleys. I don't think the composition belts produce that finish the way leather does (leather belting being like a strop).

Evan
07-22-2009, 10:47 AM
The asphalt belt dressing becomes a part of the belt surface. As I said it has the property of self activating when the belt slips and warms up. Incidentally, I just installed a new fabric/rubber belt because the serpentine belt broke finally where I had glued it. I am in the process of building up the asphalt layer on this belt which takes a while and works especially well on this type of belt. Oil doesn't make much difference to the asphalt since it acts to activate it. After all, asphalt is oil.


A good clean belt and pulleys will transmit the power they were designed for.

No. Flat belt drives were originally designed for leather belts. It was both customary and essential to use belt dressing on the belts both to condition the leather and to increase the friction coefficient.

This also applies to modern flat belts which are still widely used in applications such as conveyors and some high speed belt drives as well as specialized applications. Belt dressing is a part of regular maintenance of a flat belt drive. I worked on flat belt drive systems for 23 years. Some of the machines had multiple flat belt drives with as many as 8 six foot long 1.5" belts running on a mulitple crowned pully shaft at each end. Belt slippage is always a problem and belt dressing is the best way to prevent slippage.

JCHannum
07-22-2009, 11:35 AM
What you use is your prerogative, but belt dressing is not a necessity, and usually creates more problems than it solves. Being tacky by design, it attracts any dirt present and eventually becomes slicker than the original belt. Overuse only serves to gum up the belt and pulleys. Properly designed, installed and maintained flat belt systems will operate and track with no need for dressing or other outside means.

The South Bend HTRAL again recommends cleaning the belt and pulley with naptha or benzol and applying neatsfoot oil if the belt is dry. No mention of belt dressing.

Machinery's Handbook recommends cleaning leather belts with degreasers (A carbon tet & naptha mixture being mentioned) and applying dressing recommended by the manufacturer every three to six months to supply the natural oils lost in use or during cleaning. Neatsfoot oil would be such a dressing, asphalt based dressings would not.

Evan
07-22-2009, 11:58 AM
Overuse only serves to gum up the belt and pulleys. Properly designed, installed and maintained flat belt systems will operate and track with no need for dressing or other outside means

I suggest you do some research. Belt dressing is a multi million dollar business. In the past, at the time HTRAL was written it was standard practice to dress a leather belt not only with neatsfoot oil but with a dressing stick. Stick dressing was available in two types, brown and black. The brown was a rosin and black was asphalt. Unfortunately as far as I know those products are no longer available. Asphalt liquid in a can is still available and asphalt foundation paint works well.

Al Messer
07-22-2009, 12:05 PM
With the flat leather belt on my Logan made lathe, I run it as slack as I can and still get the needed torque when under a load. No belt dressing is used and "yes", oil does get on the belt and helps keep the leather limber.

JCHannum
07-22-2009, 12:10 PM
I have done plenty of reasearch, and have plenty of experience as well, both with flat belt conveyors and drives. There is no substitute for a properly designed, installed and maintained system. If it is not right to begin with, nothing will make it better.

The fact that belt dressing might be a multi-million dollar business and it's use might have been common practice does not preclude the fact that neither HTRAL or Machinery's Handbook recommend it's use.

lazlo
07-22-2009, 12:37 PM
Jerry, I don't have a direct answer to your question, but when I was designing the Poly-V belt drive for my Bridgeport servo retrofit I found that Gates has excellent technical resources for belt design and installation.

I spent a lot of time with their free design software (I've posted it here before), and that tells you the optimal belt tension, and predicts the belt stretch over time (depending on the material and initial tension).

If you don't want to download and install the software, they also have App Notes that walk you the correct belt tension depending on the belt type, width, RPM, etc.

Richard Wilson
07-22-2009, 01:50 PM
I suggest you do some research. Belt dressing is a multi million dollar business. In the past, at the time HTRAL was written it was standard practice to dress a leather belt not only with neatsfoot oil but with a dressing stick. Stick dressing was available in two types, brown and black. The brown was a rosin and black was asphalt. Unfortunately as far as I know those products are no longer available. Asphalt liquid in a can is still available and asphalt foundation paint works well.
With leather belts, we used to dress the outside of the belt with neatsfoot oil to keep it supple, but avoided getting directly onto the inside surface of the belt, to avoid slippage. Where possible, we just kept the inside clean and dry, and the tension correct. In emergencies, we would use a black sticky dressing to eliminate slip, it was known (in the UK Midlands) as 'Blackjack'. It looked like black treacle, but what it actually was, I never knew. The preference was just regular dressing of the outside with neatsfoot oil. I never used composition belts, so I can't comment on how they were treated.
I seem to remember that you should be able to transmit 1hp with a 1" leather belt.

Richard

Evan
07-22-2009, 02:30 PM
If it is not right to begin with, nothing will make it better.


There are a lot of machinists that will disagree with you in the steam power community, not to mention a multitude of legitimate products with legitimate claims regarding the torque increases available with belt dressing.

HTRAL is not comprehensive and only touches on various subjects, including the subject of power drive belts.

There are also many, many references that also disagree with your contention.

Just one of possibly thousands,

http://ixian.ca/pics6/beltdress.jpg



It looked like black treacle, but what it actually was, I never knew

Asphalt.

JCHannum
07-22-2009, 02:52 PM
Like any other opinion, there is probably just as much support for one side as the other. My experience and that of many, many others is that dressing is a patch for a poor set up.

Please do note that Mr. Wilson's post stated that normally dressing was not used. It was used only in an emergency situation, the preference being a regular application of neatsfoot oil.

Fasttrack
07-22-2009, 03:22 PM
From The Mechanical Engineer's Pocket-Book by William Kent:


Belt Dressings: We advise that no belt dressing be used except when the belt becomes dry and husky, and in such instances we recommend the use of a dressing. ... Our expierences convinces us that resin should never be used on leather belting (Fayerweather & Ladew)

Yes, I expect that are numerous supports for both schools of thought...

Jerry, according to Machinery's Handbook (27th Edition, page 2392):


The amount of tension varies with the belt cross-section, being greater for belts of small section. Belt tension can be measured by marking lines 10 inches apart on an installed belt, then applying tension until the separation increases by the desired percentage. For 2 per cent tension, lines on the tensioned belt would be 10.2 inches apart. Mechanical failure may result when belt tensioning is excessive, and 2 to 2.5 per cent elongation should be regarded as the limit

This was for polyurethane based composite flat belts.

J Tiers
07-23-2009, 12:20 AM
Setting the tension to 2% elongation, which I just did, produced the enormous static torque illustrated by teh following readings:

slow speed setting 250 rpm 3.8 ft-lb (belt slip tension = 26 lb, HP at speed 0.2)

medium speed setting 400 rpm 1.6 ft-lb (belt slip tension = 13lb, HP at speed, 0.15)

High speed setting 700 rpm 12 ft-oz. (belt slip tension = 9 lb, HP at speed, 0.13)

That seems not to be a good result, at least not for a 10" lathe........................ The 2% elongation may not necessarily be a reliable guide.

The belt slip tension ought to be at least 33 lb, and probably more for rubber composition. and it should be fairly constant for all pulley sizes.

Static torque is torque just before slipping of the belt, i.e. the peak reading on a scale at the end of an arm, when applying turning force to the motor's driven pulley by hand. The belt slip tension was computed by taking the ft-lb at the radius of the smaller pulley, which was invariably the one which slipped, whether it was driven or driver.

If the constant 33lb was available, the HP transmitted at each speed would be different, namely about 0.25, 0.4, and 0.7 for slow, medium, and high speeds.

JCHannum
07-23-2009, 10:07 AM
It is a bit too early to get my head around what the numbers mean, but, I would be inclined to clamp the motor leads and measure motor amps at slippage to determine horsepower supplied by the motor. It would seem that this would more closely approach actual working conditions than a static test.

Evan
07-23-2009, 11:26 AM
Jerry,

Polyurethane composite flat belts have almost no stretch. A 2 percent stretch factor is enough to make strum like a guitar string. Your numbers aren't relevant unless that is the type of belt you have. They are a very thin belt, about 1/16" to 3/32 at the most in a size for a small lathe like my SB9. The composite fabric is most often kevlar, the same as is used in cog belts to nearly eliminate stretch.

J Tiers
07-23-2009, 11:43 PM
The tension for a canvas belt to go 2% isn't a lot.

But, a proper belt and pulleys doesn't NEED much.

I am currently looking at the pulley surface, which is definitely NOT overly smooth, although I have used it for years as-is.

My father-in-law has a 9" SouthBend, and it has polished pulleys. He has a leather belt, NO belt dressing, and appears to get a LOT more torque thru it than I am getting, even tightened back up to normal.

I can take a very reasonable cut, D,O.C. wise, but he does even better.

Looks like time to polish the pulleys. The belt is grabby enough on a smooth surface, but not so much on these.