Real Sawing Speed

highpockets · December 13, 2005, 05:53:50 AM

When I first started designing my mill I read all of this hype about how fast different saws were.
Based on that I designed my feed rate. After getting the saw done, I realized that some of these numbers did not quite jive with what I was seeing. Since joing this forum I have seen several request for saw speed info.

I realize that there are many variables. Still if there was some input from different saw owners as what they are cutting in ft/min, with info such as h.p. log size, cut width, manual or automatic feed, then many may benefit. It is my opinion that some are designing the feed for fast of a cut.

DanG · December 13, 2005, 08:51:56 PM

Well, that presents a good legitimate question, but I'm not sure there is a good legitimate answer to go along with it. As you said, there are a lot of variables, so you have to make your feed rate just as variable. Not only does the optimum rate vary from species to species, it will vary from log to log, frequently from board to board, and sometimes within a board. I was cutting some pine today that had lain about for a while, so it was pretty soft at the entry end, but really sappy at the butt end. I could go into it like gangbusters, but was really crawling by the time the saw came out of it.

If I were designing a mill, it would have an infinitely variable hydrostatic drive, just like the one I have now.

highpockets · December 13, 2005, 09:04:57 PM

Dan

I agree but when I built my saw, I was looking at speeds higher than I needed and found that my 295 r.p.m. motor would not operate at speeds lower than 45 r.p.m. This is about the speed that I need to saw a 24" bull pine log. Sticky and knotty. I am guessing 15 f.p.m is the max.

Ron Wenrich · December 13, 2005, 09:21:53 PM

I'm running a circle saw, and I'm using 150 hp electric and running 690 rpm. Feed rates are dependent on a whole host of variables. It all depends on how your wood chips when it is being cut, and how well your saw can dispose of the dust.

Tulip poplar pulls a very large chip relative to hickory. The poplar is not nearly as dense. It also cleans a lot better, so I can feed a lot faster. An 8' log takes about 3 seconds to feed. The hickory may take 5 seconds. The dust has more of a tendency to spill out of the gullets and will push a saw.

If you don't have enough hp, your saw will start to saw off line, if you feed to hard. That doesn't matter if its a band or a circle. Slowing down the feed will usually correct it.

Saw sharpness plays a factor, as does the time of year. I can saw faster during the spring and fall, but have to slow down in summer and in winter. My best sawing times are in May and October.

I know this doesn't help you much in figuring out your feed rates. The saw and conditions will dictate feed rates. You just have to figure out how fast or slow you have to go to produce quality lumber. If it gets to low, then you have to figure out where the problem is at. Is it the hp, the sharpness, or the log. Some you have control over, some you don't.

Sometimes sawing is more of an art form than it is a science.

highpockets · December 14, 2005, 05:12:25 AM

Thanks Ron,
That is a lot of speed but you have a lot of h.p. If I ever get this 20 h.p. Honda hitting on both cylinders and get some decent wood, I think my rate will pick up some. I think if I were to start over on a 15 to 20 h.p rig, I make sure I could get down to 10 f.p.m. and up to maybe 100 f.p.m.

Modat22 · December 14, 2005, 08:58:52 AM

I was thinking about a weird idea the other day about feed rates. It would be neat if a person took a PLC (programmable logic controller) and had it monitor your intake manifold vacuum and blade speed then have it speed up or slow down the feed motor based on the first two variables.

As the engine governor increased throttle the vacuum in the manifold drops but the band speed remains the same, if the throttle opens and the band speed drops then the feed rate should also drop to a preset speed.

If the bandspeed and throttle variables match a certain curve the saw could let you know its time to change the blade.

This could easily be done with a cheap 60 dollar plc, vacuum transducer hollifect (sp) transducer and ether an h bridge for a dc feed motor or electric proportion valve (I don't know enough about hydraulics to judge the latter)

Sorry if I threw off the thread, I just remembered thinking about it when I read this thread.

Dan_Shade · December 14, 2005, 09:13:25 AM

delete that post, Modat22, the big boys will catch wind of that idea and run with it! you'll get screwed like the guy who invented intermittant wipers!

I do like that idea, it's a good idea.

Modat22 · December 14, 2005, 09:24:55 AM

I have a few others, no worries ;D

ronwood · December 14, 2005, 10:03:05 AM

Modat22,

I think Woodmizer LT300 looks at the current draw on the motor to control the speed. Maybe Sparks could comment on this. On my LT40 I use a tach to watch the engine rpm. I try to adjust the speed of the cut such that the motor (25hp Kohler) runs around 3550 rpm under full load.

Ron

beenthere · December 14, 2005, 10:30:47 AM

Modat22
Now that you brought this up, I'll throw in the 'link' I ran across of the new Honda snowblower that has an 'automatic' feature for 'inexperienced' users (I don't mean to throw the thread further off course, but the sawing speed question led me to thinking "if they can do it with snowblowers, it can be done with saws").
Honda release

I'm not convinced at all that taking this control of sawing speed out of ones hands is a plus, but interesting.

I've often wondered if ..... never mind, will put it in another thread sometime.

Fla._Deadheader · December 14, 2005, 11:14:33 AM

We use a Pulse Width Modulator. It is a device that sends ''spikes'' of DC Voltage to the drive motor. The faster the Pulse, the faster the speed. I only know what works for us, and that is, listen to the engine. I don't particularly care how fast I am sawing. My off bearer can only handle so much or he would be walking on his knees.

I believe that Simple is the key, no matter what system you have.

If we want to permanently increase the speed, we can change pulleys on the jack shaft that drives the carriage-sawhead.

Sawn over 200K bdft, part time, widths to 36''. That's for Cypress. Go to Live Oak and you will wait for the engine to catch up.

Don't believe anyone can answer your question with exactly what they get, unless the logs are same type, same size, same time cut and delivered to the mill. Wadda I know ??

Ron Wenrich · December 14, 2005, 05:56:29 PM

For a circle mill, the rpm of the blade has a lot to do with the sawing. If you go too slow, or too fast for the hammered speed, your saw will dish in or out. When the motor bogs down, its too late.

I imagine there is some transferable technology there between band and circle mills.

D._Frederick · December 14, 2005, 06:59:56 PM

I have an ammeter that measures the current draw for the 7 1/2 HP Baldor motor on my bandmill. I adjust the feed rate so that the motor is running at rate current. Using this method, I can sure tell when the band blade needs to be changing. I have an SCR drive on the carriage and use a potentiometer to adjust the feed rate.