A Question About Drive Belts

Comments

• James

  July 2014

  same here. I'm starting a machine shop with the SW machine shop O scale group etc. and an F scale one. There has been some discussion in the SW blog but a refresher of techniques or pitfalls would be good. One big question is how best to rig the machines etc. once the line / jack shafts have been installed- seems like things can get very tight depending on beam and shaft spacing. I was also wondering about drafting/ graphics tape (brown or black). Some seem to be the right scale width (6" +/-) and reasonably thin, but one side would be sticky and pick up dirt and lint etc.
• admin

  July 2014 edited July 2014

  As far as I am concerned there really are no tricks. It's all about the materials. The space is very confined and tight to work in so tweezers are a must. Measuring and test fitting the belt is necessary as well. About the belt material... I have tried a bunch of different types and the main concern is will it stretch over time? (Stay far, far away from anything with adhesive James!) I have found envelopes made with the dupont brand plastic material "Tyvek" to be the best material. NOT perfect, BEST. Cuts cleanly, stains great with a solvent based brown paint. It has fine random fibers that represent the creases in a leather belt as well. CA (Cyanoacrylate ie Super Glue) adheres well. Use a medium set CA, not fast to give you time to position the belt. Glue the first half to the top of the shaft wheel, allow the CA to set firmly, then wrap and glue it around the machine wheel bringing it back to the top of the shaft wheel. CA in place. Machine, machine wheel, shaft, and shaft wheel should all be set permanently and not spinning. The worst situation is a component shifts over time and the belt sags. A sagging belt looks like crap. Make sure to keep your belts taught. Use tweezers to hold the belt in place while the CA sets and trim any excess away from the top of the shaft wheel. As with most modeling techniques - easy once you try it a few times!
• silveradonorthern

  July 2014

  Thanks Brett for the information.
  You said: 'stains great with a solvent based brown paint.'
  When you say solvent base paint are you referring to paints like the old Floquil line?
  Will an oil base line like Model Master or a water base product like Vallejo work?
  I can see some possible problems with the water base paint as it 'might' cause the Tyvek to swell.
  
  Michael
• admin

  July 2014

  Gotta be a solvent based paint - no water based... Any leather brown color should work, just experiment. Let us know what you come up with!
• BrianM

  July 2014

  We cannot scale material properties so I agree with Brett that at small scale (HO, O) a flat drive belt looks better when both sides are reasonably tight than having both sides of the belt "flapping about in the breeze".
  
  However I grew up with flat belt drives on both stationary and portable equipment and based on my experience a belt that sags on a model only looks bad/wrong if the sag is either grossly excessive and/or on the wrong side (or both) of the belt and/or the belt drive incorporates a tensioning pulley.
  
  For those who are interested in some background:
  The late 18th and early 19th Century designers and operators of machinery requiring belt drives had a some challenges on high horse power applications, including: a) the plain bearings (example: bronze or Babbitt) on engines, line shafts and machines were limited in load carrying capacity even when equipped with slinger ring continuous lubrication; and b) the laced or steel comb joints (clipper or alligator style) on leather and later balatta (rubber impregnated, multi-ply woven fabric) belts limited the tension that could be applied to the belt before the joint either failed or yielded a very short service life. In regards to the latter, bear in mind that the belt joint had to handle not only the static tension but also the driven machine's starting inertia and continuously transmitted power which may also have fluctuated. Consequently they always tried to follow a few simple rules: (i) drive rotation direction to tension the bottom of the belt and have any slack on the top which increased the belt arc contact length on the pulleys which reduced pulley/belt slip (particularly important where a large pulley drove a much smaller pulley for speed increasing, or vice-versa); (ii) when the belt had to be twisted to reverse rotational direction then every effort would be made to arrange the equipment so the top side of the belt would be slack on the smaller pulley to maximize belt arc of contact; (iii) avoid vertical belts but if not possible then: run the belt at the low end of permissible speed to minimize the belt arcing away from the pulleys on the slack side due to centrifugal force; avoid small (short contact arc) pulleys; and/or consider adding a belt tensioner on the outside of the belt on the slack belt side of the drive; (iv) use a belt dressing (we used raw linseed oil) to improve adhesion between the belt and pulleys.
  
  Apologies for ambushing the thread away from Michael's belt material question.
• James

  July 2014

  wow - this is all fantastic info! Thanks for the detailed responses. I would have made some serious errors the way I was thinking. THe Machine Shop kits contain Tyvek in case some were wondering. And yes, sagging belts are prototypical- it's how they sag as noted, which would be hard to reproduce presumably- so far any sagging belts I've seen in kit builds don't look good. I recall seeing that Chuck Doan noted the belts in his machine shop are still taught after twenty+ years- I think he used Mylar.
• silveradonorthern

  July 2014

  Thanks Brian,
  For taking the time to provide all the wonderful information. I admit I know precious little about overhead belt system and machine shop tools/machines. All I know is what I've seen in a few pictures. My machine shop will only be able to handle about four machines but I think that will be enough to convey the idea.
  
  Michael
• JohnM

  July 2014

  Excellent discussion, folks . . .
  
  John
• James

  August 2014

  I'm about to rig a couple drill presses so thought I'd post this- not a great picture but the paper is drafting vellum (not as easy to find these days), spray painted brown, ready to be cut into belts. I got a couple Tyvek envelopes too so will try that as well. The vellum is a little thinner I think. It's a plastic paper like the Tyvek. I've rigged a couple things with it now and really like it.
  
  
• TonyB

  January 2015

  To open this up again with one more question, I had never known what Tyvek envelopes really were, originally thinking that they were the glassine part of window envelopes (prior to my computer searching skills). So I gave a search on the web and found they are these large envelopes like what fed-ex and others have.
  
  
  Am I right here? If so, I can probably get these at Staples or someplace, maybe.
  
  Tony Burgess
• brownbr

  January 2015

  You are right. Those work great.
• TonyB

  January 2015

  You are right. Those work great.

  Thanks Bryan, that's just what I needed to know.
  Tony
  
• James

  January 2015

  Drafting vellum works well too - as noted above. I've tried both now any they are both good options.
• MikeM

  January 2015

  Googling "drafting vellum" yields a fair number of online sources, including Amazon. Blick seems to carry a variety of special papers (anyone ever use animation paper?) that might be interesting to experiment with.
• James

  February 2015

  yeah … modern drafting vellum is plasticized cotton. It is very stable and resistant to shredding etc, YOu can get it in rolls, sheets, or pads. A couple sheets could last a hobbyist a lifetime. It's thinner than the Tyvek but has less texture.