Speed Conversion

[Tony Snyder]

Ha, I got one for smarty pants guys Babcock and bwalker. Approximately how fast would the chain speed be on a 2149 Jonsered in Feet per second, then in Furlongs per Fortnight?

 

[treeclimber165]

Depends on the sprocket, chain pitch and RPM. I could probably figure it out if I didn't have a splitting headache.

 

[Tony Snyder]

A stock 2149, about 12,500 rpm and 7 tooth, .325

Seems to me they used to publish chain speeds back about 1980 ( Husky anyway ), but I havn't seen any lately.

I figured those guys I mentioned wouldn't be able to resist the challenge.

 

[dbabcock]

I seem to remember that the drive link spacing on either .325 or 3/8 is about three quarters of an inch.

(0.75 in./1 tooth)(7 teeth/1 rev)(12,500 rev/1 min)(1 ft/12in)(1 min/60 sec) = 91 ft/sec

= 5469 ft/min
= 1.04 mi/min
= 62 mi/hr
= 100 km/hr

In land measurement:

1 "Chain" = 66 ft
1 Furlong = 10 "Chains"
1 Furlong = 660 ft

(5469 ft/min)(1 furlong/660 ft)(60 min/1 hr)(24 hr/1 day)(14 days/ 1 fortnight)= 167,053 furlongs per fortnight

This assumes that a fortnight is considered two weeks in calander days, as in 14. In old England, a fortnight was sometimes considered 10 days by the labor department. In this case, the distance the chain traveled in 10 days would be 119,323 furlongs, or about 2/3 the distance around the world!

 

[dbabcock]

To those who read what I had here before:

Please disregard the inference to consuming alcohol with pain killers. Percs and alcohol can kill you. I don't advocate drug use and I certainly wouldn't want to see anyone here harm themselves because of something I foolishly posted.

My appologies.

 

[Bill G]

I am no expert but it should be quite simple. If you take the circumference of the rim with chain multiplied by the rpm should should get the chain speed. If the diameter of the rim is 2 inches and the saw is running at 12,000 rpm it would be as follows. Circumference=2piR. (2x3.14x1)=6.28 inches. (6.28X12,000)=75,360 inches per minute or 6280 feet/minute. (6280/60 sec)=104.7 feet per second. Remember I used a 2 inch diameter rim for simplification. If the rim is actually smaller then the speed will be slower or vice-versa.

Just my random thoughts

Bill

 

[dbabcock]

Hi Bill,
I don't think the diameter of the rim needs to be included in the calculation as long as you know the distance between the drive links of the chain. If the sprocket has 7 teeth, then because it has to exactly mate with the chain drive links, it would have to move 7 drive lengths per revolution. I just measured a .325 and a 3/8 chain and they are indeed both 3/4" between drive lengths. Does this sound reasonable?

 

[treeclimber165]

Doug,
I think your 3/4" figure may be wrong. The pitch is equal to the length of one link (or the distance between three rivets divided by two). Since you have a driver every other link, the .325 chain will be .325X2 or .65". The 3/8" chain will be .375X2, or .75".

 

[dbabcock]

Brian,
You may be right. My beverages must be getting the better of me as I though when I measured them they were the same. They don't call me Babcockeyed for nothing. At any rate, I think the calculation methodology is correct, if not the measurements.

 

[treeclimber165]

Maybe you measured the same chain twice.

 

[dbabcock]

Boy did I screw up. I was actually measuring what I thought was an old .325 safety chain from the Poulan and it was actually a real small profile 3/8. So I got out the 2149, which I had just put a .325 chain on for comparison to the 3/8 I had Dennis ship it with. Yup, .65's the number. You are correct sir. I should have known that, but since I don't know anything about chainsaws or how to use them, I have an excuse. Anyway, Here are the new numbers for a .325:

79 ft/sec
4739 ft/min
0.898 mi/min
53.9 MPH
86.9 KPH

144,053 furlongs/fortnight (14 day measure)
103,396 furlongs/fortnight (10 day measure)
12,925 miles/fortnight (10 measure)

Thanks Brian.

 

[dbabcock]

I just thought of something. I know that link 2X spacing thing. Moreover, if they were the same, then why did I have to get a different sprocket when I switched over to the .325. Doh! I need a drink.