From: mfolenta@PICA.ARMY.MIL (Michael Folenta (FSA) <mfolenta>)
Newsgroups: rec.woodworking
Subject: Re: Wormdrive saws
Date: 20 Nov 92 17:20:18 GMT
Reply-To: mfolenta@pica.army.mil
Organization: US Army Armament, Research, & Development Center



 In article <1992Nov18.203849.12802@schaefer.math.wisc.edu>, (Bob Wilson)
writes:
> wesw@hpmwtd.sr.hp.com (Wes Whiteley) writes:
> 
>>/ hpmwmkt6:rec.woodworking / Jeff Roberts  /  7:47 am  Nov 13, 1992 /
>>>
>>Would anybody out there consider explaining the details of these saws
such
>>as application, why it's called "wormdrive" etc.  I'm not familiar with
>> them.
> 
>>Jeff Roberts  JROBERTS@UTDALLAS
>>----------
> 
>>  Jeff,
> 
>>  I don't have all the details, but here is the the basics.
> 
>> On a normal circular saw, the motor's shaft is directly (i.e. NO gears)
>> connected to the saw blade. On a worm drive saw the blade is connected
to 
>> the motor via a set of "worm" gears.  The biggest advantage of these
saws
>> is the increase in torque as a result of the gear ratios.  The
drawbacks
>> are: 1) a heavier saw. 2) a little more maintenance (the gear oil has to
>> be changed occasionally - depending on usage).
> 
> 
>>  Good luck,
> 
>>  wes
>
> I think the "no gears" statement is almost always wrong. The typical
> universal motor in one of these saws turns way too fast for the blade
> and is geared down. Better saws probably use helical cut gears, to
> minimize the noise as much as anything else, but they definitely use
> gears. (Easy to check without disassembly or looking in parts diagram:
> Turn the blade while looking into a ventilation slot. With one stage
> of gearing, as is common, the motor and the blade turn opposite
> directions.)
> I did read a review of circular saws which had ONE MODEL without
> gears, using a special motor which would develop enough torque at
> lower RPM. I don't recall which model that was but it was unique, the
> counterexample which proves the theorem.
> The worm gear in fact is probably a little LESS efficient at
> transmitting power, because of the greater friction, but when properly
> done (they run in an oil bath, the regular gears are in air with just
> some grease smeared on the teeth) this isn't great. The big advantages
> seem to come primarily from the fact that the worm-drive has a 90
> degree bend in it, so the motor armature runs front-to-back rather
> than across the cut. This changes the balance as well as where the
> motor is blocking visibility. I suspect another difference is just
> that a manufacturer will probably put more quality into something
> selling in the higher price class, although that is certainly not
> always true.
> Bob Wilson
> wilson@math.wisc.edu
 
 
 
      Well, Wes is wrong and Bob is right (about gearing anyway).
  But Wes did have the general gist of the advantages (more blade 
  torque) and disadvantages (heavier and more maintenance) of worm 
  drive saws compared to regular circular saws.
 
      Your normal run-of-the-mill circular saw has gears in it.  These
  gears are usually spur or helical gears with grease (and sawdust - 
  after you use it ;-} ) lubrication.  Any bearings in the saw are 
  probably also grease lubricated.  Decent spur gears are about 96%
  efficient in transmitting power through the mesh and helical gears
  would be slightly less efficient (but they are usually quieter than
  spur gears), say maybe 93% efficient.  These gears types will have
  parallel shafts, meaning that the motor shaft and the blade shaft
  will be parallel to on another.  This arrangement of shafts means 
  that the motor hangs out/off the side of the saw as in a typical
  circular saw.
 
      A saw with worm gearing has the shafts at a 90 degree angle 
  (typically), which means the motor axis is in-line with the handle
  and the saw is long and narrow compared to a regular circular saw
  which is short and wide.  A worm drive saw typically has an oil
  bath lubrication system (less sawdust in with the gear teeth).
  A worm gearing system can be 75-90% efficient, but it lets you
  have a LOT of reduction in speed in each stage.  This lets the
  manufacturer 'gear down' the motor's RPM and get some more
  torque out of the combination (remember that torque x rpm = power).
  If you check the blade rpm rating on some different circular saws,
  you'll find that regular circular saws (7 1/4") spin the blade at
  about 5000 rpm (no load speed) and a worm drive saw will spin the 
  blade at about 4500 rpm (no load speed). 
 
      They will both cut and they will both do the job (usually), so get 
  whichever one you want.  The worm drive saw might be considered to a 
  little more 'heavy duty' and you usually pay for that (also there are 
  less worm drive saws made and sold, so you pay more there too).  The
  worm drive saws are usually heavier also (can be good or bad) and have
  a different balance/feel to them than the other type of saw.  For a
  righty, the cut line is also more visible with a worm drive saw.
 
      Like I said, get whichever one you want and are confortable with.
  They will both work.  Me, I'm using a run of the mill circular saw
  for now.  It works and does the job OK (but boy does that thing
SCREAM!).
 
 
-- 
       ***** These are my opinions.  Get your own. :-) *****
      Michael Folenta          | U.S. Army ARDEC
   Future Weapons Branch       | Picatinny Arsenal, NJ 07806-5000
  email mfolenta@pica.army.mil | (201) 724-3880  [AV 880-3880]
Newsgroups: rec.woodworking