The Forestry Forum is sponsored in part by:




TimberKing Sawmills




Toll Free 1-800-582-0470

LogRite Tools



Forest Products Industry Insurance


Norwood Industries Inc.


Sawmill & Woodlot Magazine



Your source for Portable Sawmills, Edgers, Resaws, Sharpeners, Setters, Bandsaw Blades and Sawmill Parts

EZ Boardwalk Sawmills. More Saw For Less Money!

STIHLDealers.com sponsored by Northeast STIHL


Woodland Sawmills

Peterson Swingmills

 KASCO SharpTech WoodMaxx Blades


Turbosawmill

Sawmill Exchange

BRUTE FORCE Authorized Dealer

Woodshax Outdoor Vending Solutions

FARMA


Council Tool

Baker Products

Forestry Forum Tool Box

Author Topic: chain sprocket size?  (Read 2939 times)

0 Members and 1 Guest are viewing this topic.

Offline bedway

  • Senior Member x2
  • *****
  • Posts: 1043
  • Location: northwest pa. south of erie
  • Gender: Male
  • I'm new!
chain sprocket size?
« on: November 27, 2007, 06:38:44 pm »
Im trying to calculate whats the biggest size sprocket i can put on my 12 volt gearmotor to raise my saw head as fast as possible, yet not over tax the motor? The head has two acme threaded rods with 5 threads per inch. I tack welded a nut on one of the rods,above the sprocket and it took 5 footpounds with a torque wrench to raise the head. That equates into 60 inchpounds if im correct. The gear motor is rated for 100 inchpounds. The gearmotor turns 25 rpm. That tells me in one minute the head would raise 5 inches, if i have a 12 tooth sprocket on the motor, which is whats on the acme rods. This, unless im wrong means the motor would take 4 plus minutes to raise the head 20 plus inches. Can anyone help me on this?,,,bedway

Offline Gary_C

  • Senior Member x2
  • *****
  • Posts: 6079
  • Age: 75
  • Location: Blooming Prairie, MN USA
  • Gender: Male
  • Sunrise on the Prairie
Re: chain sprocket size?
« Reply #1 on: November 27, 2007, 07:10:35 pm »
If you went to a 20 tooth sprocket you would boost the torque to the 100 lbs maximum and reduce your time to 2.4 minutes total for 20 inches. However the starting torque may be more than the motor can handle at that 20 tooth sprocket size. So to be safe you could use an 18 or 19 tooth if you could find one. An  18 tooth would increase your torque and speed by 1.5 times and reduce your time to 2 minutes, 40 seconds for full travel.
Never take life seriously. Nobody gets out alive anyway.

Offline bedway

  • Senior Member x2
  • *****
  • Posts: 1043
  • Location: northwest pa. south of erie
  • Gender: Male
  • I'm new!
Re: chain sprocket size?
« Reply #2 on: November 27, 2007, 07:59:41 pm »
You will have to bear with me on this one because my son in law and i have been debateing/argueing over this for the last several hours. He says the size of the sprockets on the rods are not relative. I realize the two critical factors are the amount of torque required to lift the head, and the torque rateing on the motor. My thinking is if it requires 60 inchpounds to lift the head. Then the motor in theory has 40 % capacity left. That being said, 40 % of 12 is 4.8, so my reasoning says it could take,,in theory a sprocket with 16.8 teeth. In reality a 17 tooth sprocket would be 2% beyound the motors ability! I guess im lost where you got the 20 tooth sprocket size from Gary? I know some of you math and or engineering wizards should eat this up in a second,,bedway

Offline Firebass

  • Senior Member
  • ****
  • Posts: 347
Re: chain sprocket size?
« Reply #3 on: November 27, 2007, 08:25:17 pm »
torque (foot LBS) = (5252/hp)/RPM

Multiply by 12 to get the inch lbs.

What this is basicly saying is it's not the torque that is unchievable its the reasonable speed.

Kind of thin but maybe it'll help.

Firebass

Offline Gary_C

  • Senior Member x2
  • *****
  • Posts: 6079
  • Age: 75
  • Location: Blooming Prairie, MN USA
  • Gender: Male
  • Sunrise on the Prairie
Re: chain sprocket size?
« Reply #4 on: November 27, 2007, 09:01:25 pm »
Your son in law is right, the sprocket size on the rods for this calculation is irrelevant. What you need to do is increase the motor load from 60 in-lbs to 100 in-lbs so you use the ratio of 100/60 and multiply that times the existing sprocket size of 12 teeth. That gives you 20 teeth for the new sprocket. But that is the theoretical maximum you should use if everything stays the same.

In this case friction is very important and may not stay the same because of lubrication on the rods, rust, dirt, and sawdust. So you should not go up to the calculated 20 tooth sprocket. Also the motor may not have enough starting torque to start the rods turning so thats why I suggested an 18 tooth sprocket that would give you a theoretical increase from 60 to 90 in-lbs.

But that 18 tooth is just an educated guess. It's best to try that sprocket and measure the motor current and compare that with the max rated motor current.
Never take life seriously. Nobody gets out alive anyway.

Offline bedway

  • Senior Member x2
  • *****
  • Posts: 1043
  • Location: northwest pa. south of erie
  • Gender: Male
  • I'm new!
Re: chain sprocket size?
« Reply #5 on: November 28, 2007, 09:13:47 am »
Thanks for the replies guys. Im following you now Gary. I think ill hunt down a 17 or 18 tooth sprocket and give it a try. As you suggested, checking the draw on the motor,,bedway

Offline Stephen

  • Full Member
  • **
  • Posts: 55
  • Age: 51
  • Gender: Male
  • Glad to be part of a great group.
Re: chain sprocket size?
« Reply #6 on: November 29, 2007, 11:43:00 am »
Now slow down a bit Bedway. I read kind of slow and type even slower.

If you have more torque than you need, and want to speed things up a little, you need about an 8 tooth sprocket on your driven shaft. However as previously stated, you may want some lee-way for starting torque and friction as the sawdust builds up. I am thinking 10 or 12, if you want faster, you need a smaller sprocket than whats on the motor.
Sound to me like you may need a bigger motor.

Stephen
1994 WoodMizer LT40G18. 69 acres mixed wood. 1952 ford tractor, Norse 290 winch, studed Norse ice chains. 45-66DT Fiat.

Offline bedway

  • Senior Member x2
  • *****
  • Posts: 1043
  • Location: northwest pa. south of erie
  • Gender: Male
  • I'm new!
Re: chain sprocket size?
« Reply #7 on: November 29, 2007, 02:59:05 pm »
Stephen,,, The acme rods each have 12 tooth sprockets allready on them. They are linked together with #40 chain with a idler adjustment for tension. After sawing several hundred board feet with one of the rods haveing a crank/handle on it,,,,,,,,it got old an tireing real fast! Haveing to crank it 100 plus times to bring the head from the bottom to the top, plus it being high (because i mounted my mill on an axle) wore me out. The new 12 volt gearmotor i got off ebay has 100 inlbs torque rateing. Im just trying to decide the size of the sprocket to put on the motor. What Gary is saying (and somebody correct me if im wrong) is that if all three sprockets were 12 tooth, and that we know it takes 60 inlbs. to raise the head, then it means the gearmotor is only needing 60 inlbs. of its 100 inlbs. capacity. Theory says if i go up to a 20 tooth sprocket on the gearmotor, then ive used all the motors ability. As previously stated friction etc. becomes a factor, and something less than a twenty tooth would be more reasonable.,,,,,,,,,anyway,,whos on first,,,,no,,hes on second :D,,,,,bedway

Offline bedway

  • Senior Member x2
  • *****
  • Posts: 1043
  • Location: northwest pa. south of erie
  • Gender: Male
  • I'm new!
Re: chain sprocket size?
« Reply #8 on: November 29, 2007, 03:02:58 pm »
BTW,,I have several pics of my mill in my gallery,,,bedway

Offline scrout

  • Full Member x2
  • ***
  • Posts: 124
  • Location: Oregon
Re: chain sprocket size?
« Reply #9 on: November 29, 2007, 04:31:22 pm »
Hi Bedway,

Nice mill....I just got my 190A kit, but sawframe only so I still have to fab exactly what you are speaking of.
On the torque/speed issue, if you are 1:1 ratio on sprockets, you get the same speed and same torque of your gearmotor applied to the acme shaft.
If you go 20:12, you have a 166% speed increase, but your torque amplification is opposite and would only be 60%, and it is not clear your motor would handle that.
What you want to do is have a faster motor with a small sprocket to a larger driven sprocket.
For example, a 300 rpm motor thru a 3:1 (like 8 to 24) would run the rods at 100 rpm, and you would get a 3x (minus efficiency of the system) torque increase, so a 50 in lb motor would be applying closer to 150 in lbs at the rod.
Unfortunately, all the real world variable like friction, etc. means that you will need to take your best guess and then try it.
Please let us know what you find out, cuz is sounds like I am going to get tired of cranking too!!

Offline logwalker

  • Senior Member x2
  • *****
  • Posts: 1629
  • Age: 66
  • Location: San Juan Island, WA 98250
  • Gender: Male
  • Got Logs??
Re: chain sprocket size?
« Reply #10 on: November 29, 2007, 07:26:47 pm »
I have been trying to follow this and I have a question. If the gearmotor has a shaft that can accept different sprockets, how does the manufacturer rate the inch-pounds? Is it the torque at the diameter of the shaft or at a specified diameter?

Also what is the HP rating of the gearmotor? My gut is telling me it is too small. Joe
Let's all be careful out there tomorrow. Lt40hd, 22' Kenworth Flatbed rollback dump, MM45B Mitsubishi trackhoe, Clark5000lb Forklift, Kubota L2850 tractor

Offline Brucer

  • Senior Member x2
  • *****
  • Posts: 4134
  • Age: 68
  • Location: Rossland, BC
  • Gender: Male
  • The Kootenay Sawyer - retired (for now)
Re: chain sprocket size?
« Reply #11 on: November 29, 2007, 11:40:43 pm »
logwalker:

Torque is the rotating equivalent of force. It doesn't vary with shaft diameter, sprocket size, pulley size, etc. That's why it's used for rating motors (especially gearmotors).

The size of sprocket you put on the shaft determines how much force is applied to the chain.
Bruce    LT40HDG28 bandsaw with two 6' extensions.
"Complex problems have simple, easy to understand wrong answers."

Offline Stephen

  • Full Member
  • **
  • Posts: 55
  • Age: 51
  • Gender: Male
  • Glad to be part of a great group.
Re: chain sprocket size?
« Reply #12 on: November 30, 2007, 11:24:58 am »
Right Bedway.
:PYea, reading the original post again, it makes more sense. ::)
I just seen "i have a 12 tooth sprocket on the motor", didn't notice the "if" part in front it.
With friction factored in, I still would keep the ratio close to 1:1.
1994 WoodMizer LT40G18. 69 acres mixed wood. 1952 ford tractor, Norse 290 winch, studed Norse ice chains. 45-66DT Fiat.