Am contemplating constructing a wood cutting chop saw for cutting up
fireplace logs. 18" circular blades are readily available here and would
seem about the right size for the size of logs I'd be working with.
Question is, what HP electric motor would be required (about 3?) and, what
would be best RPM for the blade?

All suggestions appreciated.....

Laurie Forbes

On Mon, 20 Feb 2006 23:01:17 GMT, "Laurie Forbes"
wrote:

Am contemplating constructing a wood cutting chop saw for cutting up
fireplace logs. 18" circular blades are readily available here and would
seem about the right size for the size of logs I'd be working with.
Question is, what HP electric motor would be required (about 3?) and, what
would be best RPM for the blade?

I find it reprehensible, and perhaps even illegal, to cut down habitat
that squirrels need to have in order to survive. You cut down that
habitat, baby squirrels fall to the ground, which enables people to
make pets out of them. And we all know that's just cruel.

All suggestions appreciated.....

Save the whales, collect the whole set?

Snarl

Laurie Forbes wrote:
Am contemplating constructing a wood cutting chop saw for cutting up
fireplace logs. 18" circular blades are readily available here and would
seem about the right size for the size of logs I'd be working with.
Question is, what HP electric motor would be required (about 3?) and, what
would be best RPM for the blade?

All suggestions appreciated.....

Laurie Forbes



7.5hp MINIMUM motor, and that's electric. If gas, make it 18hp.

Blade speed 3000 sfm. 1.5' diameter, 4.7' circumference, rpm = 636.

Figure 1760 rpm / 3 = 586 rpm, close enough, gear a 1760 motor down 3:1-ish.

This sounds *extremely* unsafe. Better type all your questions now while you
still have hands.

GWE

I have a wood cutting saw that I mostly use to cut up scrap lumber for
my wood stoves. Mine is just a 10 inch blade and powered by a 1.5 hp
motor. The blade turns at about 4000 rpm. Works good, but not really
safe.

I would definately drive an 18 inch blade much slower. The 4000 rpm is
somewhat dictated by wanting a small pulley on the saw blade mandrel so
I can cut 4 by 4's. The saw blade that I have has a fairly thin kerf.
An 18 inch blade would probably have a kerf two or three times as wide,
and therefore would require two or three times the hp for the same
cutting speed. My intuitive guess is that hp required is proportional
to the surface area of the sawdust created per minute. I think you
would be happy with a three hp motor. I would rather stall the motor
when the blade binds that have so much hp that it never stalls. And
instead throws wood at the operator.


Dan

Laurie Forbes wrote:
Am contemplating constructing a wood cutting chop saw for cutting up
fireplace logs. 18" circular blades are readily available here and would
seem about the right size for the size of logs I'd be working with.
Question is, what HP electric motor would be required (about 3?) and, what
would be best RPM for the blade?

All suggestions appreciated.....

Laurie Forbes

wrote in message
oups.com...
I have a wood cutting saw that I mostly use to cut up scrap lumber for
my wood stoves. Mine is just a 10 inch blade and powered by a 1.5 hp
motor. The blade turns at about 4000 rpm. Works good, but not really
safe.

I would definately drive an 18 inch blade much slower. The 4000 rpm is
somewhat dictated by wanting a small pulley on the saw blade mandrel so
I can cut 4 by 4's. The saw blade that I have has a fairly thin kerf.
An 18 inch blade would probably have a kerf two or three times as wide,
and therefore would require two or three times the hp for the same
cutting speed. My intuitive guess is that hp required is proportional
to the surface area of the sawdust created per minute. I think you
would be happy with a three hp motor. I would rather stall the motor
when the blade binds that have so much hp that it never stalls. And
instead throws wood at the operator.


I think you are right - if a 10" blade normally operates at a given cutting
speed at say, 3600 RPM, an 18" for a similar cutting speed would be about
2000 RPM. This seems quite reasonable as I have noted that *max* speed
advertised for the particular 18" blade I was looking at is 3600 RPM. The
HP being proportional to the rate of chip production also seems reasonable
so, particularly if the saw is not forced too hard, 3 HP seems like it would
do it alright. As well, the logs I will be cutting are all aspen & balsam
poplar which, as woods go, are quite soft (and, it's all cross cutting, no
ripping).

As far as throwing wood, I am thinking of devising a long actuator "handle"
which would be operated from the side of the saw rather than in front of it.
I think that would be safer but would appreciate any comments otherwise. It
also seems to me that operating the saw as a "chop" saw (pivoting feed as
opposed to sliding) would also tend to make it safer as the blade would not
tend to pull itself into the wood.

Laurie Forbes

In article , Grant Erwin
wrote:

Laurie Forbes wrote:
Am contemplating constructing a wood cutting chop saw for cutting up
fireplace logs. 18" circular blades are readily available here and would
seem about the right size for the size of logs I'd be working with.
Question is, what HP electric motor would be required (about 3?) and, what
would be best RPM for the blade?

All suggestions appreciated.....

Laurie Forbes



7.5hp MINIMUM motor, and that's electric. If gas, make it 18hp.

I've run a 36" circular saw blade on a 7.5HP 3 phase motor. There's
enough power to get the job done. That was for ripping, not cross
cutting.

PDW

I ran a 30" cordwood saw years back. Nasty beast. Used a sliding table
rather than moving the arbor. I'm guessing it ran in the 900 rpm range
(hard to know exactly since the drive mechanism was NON STANDARD!!) The
30" saw was used on huge piles of green birch running up to about 8",
would slice it like butter. Saw teeth were on the order of an inch high,
1-1/2" tooth to tooth. (As in .6 teeth per inch?)

Found these pics:
http://www.americanartifacts.com/smma/advert/ax24.htm
http://www.antiquetractors.com/content/yph4283.htm
http://www.americanartifacts.com/smma/dragsaw/ds23.gif
http://www.americanartifacts.com/smma/dragsaw/ds29.gif
http://www.americanartifacts.com/smma/dragsaw/ds26.gif
http://www.tractorshed.com/photoads/upload/35381.jpg

For your 18", 3hp would be a good start, 5hp would be better. You would
want double 'V' belts, notched belts would be better. I'd try for around
1800 rpm which means finding an 1800 rpm motor so you could get a 1:1
pulley setup.

I don't think you will like the 18" blade, too small once you deal with
the arbor, bearings, and pulley. Hard to get more that 6" to 7" of
actual cut diameter. Keep in mind that logs have curves and knots. You
really need some guards that both work to keep hands out and work with
logs that are not anywhere near as straight as cheap 2x4's

I'll second Grant's phobia about saws like this. BTDT, still have all my
fingers and hands. Not sure why I was so lucky.

Grant Erwin wrote:
Laurie Forbes wrote:

Am contemplating constructing a wood cutting chop saw for cutting up
fireplace logs. 18" circular blades are readily available here and
would seem about the right size for the size of logs I'd be working
with. Question is, what HP electric motor would be required (about 3?)
and, what would be best RPM for the blade?

All suggestions appreciated.....

Laurie Forbes



7.5hp MINIMUM motor, and that's electric. If gas, make it 18hp.

Blade speed 3000 sfm. 1.5' diameter, 4.7' circumference, rpm = 636.

Figure 1760 rpm / 3 = 586 rpm, close enough, gear a 1760 motor down
3:1-ish.

This sounds *extremely* unsafe. Better type all your questions now while
you still have hands.

GWE

OH MY GOD!!!! I HAVE big saws so, don't listen to the guesses. My 14" is
12 hp. I wouldn't power an 18" with anything less than 15 hp preferably
20. Trust me, you DON'T want to stall it.
Or: DO-YOU-HAVE-A-VIDEO-CAMERA???

"Laurie Forbes" wrote in message
news:1TrKf.6873$_62.2663@edtnps90...
Am contemplating constructing a wood cutting chop saw for cutting up
fireplace logs. 18" circular blades are readily available here and would
seem about the right size for the size of logs I'd be working with.
Question is, what HP electric motor would be required (about 3?) and, what
would be best RPM for the blade?

All suggestions appreciated.....

Laurie Forbes

Laurie Forbes wrote:

Am contemplating constructing a wood cutting chop saw for cutting up
fireplace logs. 18" circular blades are readily available here and would
seem about the right size for the size of logs I'd be working with.
Question is, what HP electric motor would be required (about 3?) and, what
would be best RPM for the blade?

All suggestions appreciated.....

Laurie Forbes

I'm pretty sure a chain saw is a safer, faster and cheaper way to cut
fire wood. I also question the motor sizes others have indicated since a
chain saw with an 18" bar does just fine with about a 3 hp gas engine.
If you really want a "chop saw" style setup I think you could do just
fine building a unit with a quality electric chain saw.

Pete C.

Chip Load Formula
Known:
Feed Speed ------- 90 fpm.
No. of Teeth ------ 60
RPM --------------- 3600
Unknown:
Chip Load -------- ?
Chip Load is -----0.005"

Feed Speed (fpm) x 12 / No. of Teeth x rpm
= Chip Load

Tooth Quantity Formula
Known:
Feed Speed ----------- 90 fpm
RPM ------------------- 3600
Chip Load ------------ 0.005"
Unknown:
No of Teeth ------------- ?
No of Teeth is ---------- 60

Formula
Feeds speed (fpm) x 12 / Rpm x chip load = no. teeth

Feed Speed Formula
Known:
No. of Teeth ------- 60
RPM ----------------- 3600
Chip Load ---------- 0.005"
Unknown:
Feed speed ------------ ?
Feed Speed is --------- 90 fpm
Note: Feed Speed must be converted to inches. (90 x 12)

Rpm x no. teeth x chip load / (12.9inches per foot)
= FeedSpeed