Electric Chainsaw Mill with load regulation

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wileur

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Hi,

I'm in the middle of building an electrical chainsaw mill. Since I have a background in industrial automation, electronics development and embedded programming I decided to automate things quite a bit.
I'm going to use a 5.5kW three-phase motor to power the saw, a smaller motor for feeding and and a 24V geared DC-motor with wires and pulleys to lift the saw head. An optical rotary encoder will help keep track of the height.
The bigger motors will be controlled by two frequency drives I had laying around. I'll put some inductive sensors to act as limit switches to automatically turn of the saw and feeding when reaching the end of the log.
The rails and log bed will somewhat resemble a Norwood PM14, but the saw carriage will be different as I'll be using parts of a pallet wrapping machine.
Most of the electronics has been completed while waiting for other parts to arrive and I have welded most of the motor mount.
Instead of a very expensive 6m drag chain I'm thinking to tie several cables together to form a stable flat cable.

Now to my question/thought: Would it make sense to adjust the feed rate based on the main saw motor load? Since I use VFDs and modbus communication I can easily monitor current, power draw or rpm and should be able to continuously adjust the feed rate to accommodate for varying log thickness, dryness, density, knots etc. If the saw starts to bog down, the system will slow down the feed a bit. Likewise, if it cuts like through butter it can move faster.
From my experience in using an alaskan mill this sounds like a good idea, but I might be overthinking it.


Best regards,
Wileur
 
From my 18th century gun barrel reaming experience: pulling the saw through the log with a weighted cable would do the job... on a wide log, or a hard one, or one with knots, the feed would slow down without any attention. See the video at about the 5 minute point for an example of an associate of mine using the technique... We had a different but similar reaming machine when I worked there.

Mixing some 18th century tech with some 21st century tech would be an interesting contrast. 😉
 
From my 18th century gun barrel reaming experience: pulling the saw through the log with a weighted cable would do the job... on a wide log, or a hard one, or one with knots, the feed would slow down without any attention. See the video at about the 5 minute point for an example of an associate of mine using the technique... We had a different but similar reaming machine when I worked there.

Mixing some 18th century tech with some 21st century tech would be an interesting contrast. 😉

Interesting video! The weight and rope idea is good and I saw a guy on YouTube use it with his Alaskan mill and it worked well.
It was my original plan too, but I like automation so I added a motor for feeding the carriage.

My takeaway then is that constant pressure is worth the effort, so I'll look more into that.
Thanks!
 
My experience with a carriage-mounted CSM also supports the idea of load-sensing variable carriage speed, I push the carriage by hand deliberately so I can maintain a constant load and consistent chain speed. It seems to give me a cleaner and more consistent surface.
 
Interesting video! The weight and rope idea is good and I saw a guy on YouTube use it with his Alaskan mill and it worked well.
It was my original plan too, but I like automation so I added a motor for feeding the carriage.

My takeaway then is that constant pressure is worth the effort, so I'll look more into that.
Thanks!
Ceteris paribus, consistent pressure via a variable feed rate captures the notion a bit more fully... I'd think that constant pressure alone could overwhelm the saw's ability to cut some times and leave it operating at below capabilities levels at others...
 
A load cell rigged to engine mounts on a simple pivot or something RPM related as a speed controller on the feed rate was my best idea. Not sure if it's practical. Load cells are expensive if you buy stuff Baha1000 race ready quality parts. This is how a modern water brake dyno works. Calculate the torque and get all the info. Maybe watch your exhaust gas temps also. Another way to control load based on head temps.
 
Ceteris paribus, consistent pressure via a variable feed rate captures the notion a bit more fully... I'd think that constant pressure alone could overwhelm the saw's ability to cut some times and leave it operating at below capabilities levels at others...
Yes, you are right. I was thinking more along the lines of consistent load on the motor, by varying the feed rate.

A load cell rigged to engine mounts on a simple pivot or something RPM related as a speed controller on the feed rate was my best idea. Not sure if it's practical. Load cells are expensive if you buy stuff Baha1000 race ready quality parts. This is how a modern water brake dyno works. Calculate the torque and get all the info. Maybe watch your exhaust gas temps also. Another way to control load based on head temps.
I believe I have a pretty good way of monitoring the load. Since I'm using an electric motor with a Variable Frequency Drive with Modbus communication to my controller I can continuously read the load power or current.
 
A few random pics of the project.
 

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Yes, you are right. I was thinking more along the lines of consistent load on the motor, by varying the feed rate.


I believe I have a pretty good way of monitoring the load. Since I'm using an electric motor with a Variable Frequency Drive with Modbus communication to my controller I can continuously read the load power or current.
That is reading the saw head combined with drive effort not one or the other.
 
@Lightning Performance:
I might be missing something here, but isn't it enough to read the saw head load? Why drive effort?

As I wrote above, I'm using three-phase 400V asynchronous motors for the saw head and feed, controlled by sensorless vector VFDs. My understanding is that if I tell the VFD to run the motor at its nominal frequency of 50Hz, it will try to maintain this speed under varying loads by pushing more or less power into the motor.
My assumption is that motor load is basically affected by wood hardness and feed rate. Of these I can control the feed rate.
(Chain condition might also affect things, but I'll change/sharpen the chain when I get saw dust instead of chips.)

The feed motor is also controlled by a VFD, which strives to keep the feed constant at the rate my system sets. So as long as I have enough power headroom I consider the feed rate to be an output variable, instead of something to be measured.


So, in short, both VFDs+motors will automatically try to stay at their set points, and I'll adjust the feed rate set point based on the motor load reading.


If this is still the wrong way to go about it, please let me know. I'm happy to improve and learn.
 
That is reading the saw head combined with drive effort not one or the other.
I realize after considering my reply that the system actually does what you suggest. The feed drive effort is managed directly by the control loop between the VFD and motor.

Thanks for making me think!
 
I realize after considering my reply that the system actually does what you suggest. The feed drive effort is managed directly by the control loop between the VFD and motor.

Thanks for making me think!
It's just like you're driving it with both controllers.
You got this pretty much figured out.
I'm thinking it's worth copying. If you're nearby and something does go wrong no big deal. The load cell can be used as fail safe kill switch for a full stop.
 
Hi,

I'm in the middle of building an electrical chainsaw mill. Since I have a background in industrial automation, electronics development and embedded programming I decided to automate things quite a bit.
I'm going to use a 5.5kW three-phase motor to power the saw, a smaller motor for feeding and and a 24V geared DC-motor with wires and pulleys to lift the saw head. An optical rotary encoder will help keep track of the height.
The bigger motors will be controlled by two frequency drives I had laying around. I'll put some inductive sensors to act as limit switches to automatically turn of the saw and feeding when reaching the end of the log.
The rails and log bed will somewhat resemble a Norwood PM14, but the saw carriage will be different as I'll be using parts of a pallet wrapping machine.
Most of the electronics has been completed while waiting for other parts to arrive and I have welded most of the motor mount.
Instead of a very expensive 6m drag chain I'm thinking to tie several cables together to form a stable flat cable.

Now to my question/thought: Would it make sense to adjust the feed rate based on the main saw motor load? Since I use VFDs and modbus communication I can easily monitor current, power draw or rpm and should be able to continuously adjust the feed rate to accommodate for varying log thickness, dryness, density, knots etc. If the saw starts to bog down, the system will slow down the feed a bit. Likewise, if it cuts like through butter it can move faster.
From my experience in using an alaskan mill this sounds like a good idea, but I might be overthinking it.


Best regards,
Wileur
Hi Wileur I have some similar experience in the plastics extrusion automation.
Also built a hydro drive for a chainsaw mill.
I found with the power feed on the CS mill the Echo would start to bog for any number of reasons. Therefore a “full on” throttle snd slow feed allowed one to walk away and stack boards.
Point being to avoid need to do a quick reverse to avoid a lock up.
Easy with a hydro drive , if you are hands on…..

Load sensing feedback via the VFD is excellent and personally I think it would be A1. Not for me tho as I suck at the programming, based on an old Hitachi 300 VFD-10 hp.

Not sure how big a slab you have in mind but personally I’d go big chain big bar big power less program.

5 kw if 2 pole motor has a sharp torque drop off making the sweet point narrow.
If 1800 rpm still likely get good chain speed-feed balance maybe easier control?

RE chain feed: I use the same hydro drive from a Sears ride on and an AC motor thru to dual chain drive down each side of the carriage.
Chain is #40 several 10 ft. Joined to make long enough for a 21 ft. Carriage (on swing blade now)
#40 chain joined to make 45 ft. Chain HAS to be laid side and stretched. Even if links are same number there can be at least a 1/2 link difference!
This causes real grief in feed.

I switched to Oregon power cut chain, regular crosscut, refilled to 10/10 degrees, cheap, works great. Cut is quite a bit rougher. A chisel refilled will give an almost smooth cut, 80% as good as bandsaw.

Nothing like hands off cutting. Or is that cutting off…
Might be good to add interrupt beam to each side of carriage as personal and last ditch end stop. I have used the orange coloured little projectors and a driveway type reflector on past projects.

Every log is like a Christmas present!
 
Load sensing feedback via the VFD is excellent and personally I think it would be A1. Not for me tho as I suck at the programming, based on an old Hitachi 300 VFD-10 hp.
I'm itching to get all the mechanical parts together so I can see how well it really works.
Not sure how big a slab you have in mind but personally I’d go big chain big bar big power less program.
My average logs are ca 25-30cm/10-12" spruce, with a few bigger ones. I bought a 63cm/24" bar, which should be plenty.
5 kw if 2 pole motor has a sharp torque drop off making the sweet point narrow.
If 1800 rpm still likely get good chain speed-feed balance maybe easier control?
I'll let the VFD keep the chain speed constant. Let's say it needs 6A to run full speed with no load and can handle a max of 11A, then I'll vary the feed rate to keep the saw load within the limits.
One advantage of using AC 3-phase motors is that they provide good torque at most RPMs. A gas chainsaw needs very high revs to provide the same cutting power.
In my case the motor runs at 1450RPMs at 50hz.

RE chain feed: I use the same hydro drive from a Sears ride on and an AC motor thru to dual chain drive down each side of the carriage.

Chain is #40 several 10 ft. Joined to make long enough for a 21 ft. Carriage (on swing blade now)
#40 chain joined to make 45 ft. Chain HAS to be laid side and stretched. Even if links are same number there can be at least a 1/2 link difference!
This causes real grief in feed.
I'm still looking through my drawers and considering options, but I've almost decided on a 400W permanent magnet AC servo motor that I'll gear down a bit. I'm thinking to start with a larger drive wheel and a wire down the center, but to switch to a chain if it slips.
I switched to Oregon power cut chain, regular crosscut, refilled to 10/10 degrees, cheap, works great. Cut is quite a bit rougher. A chisel refilled will give an almost smooth cut, 80% as good as bandsaw.
Logosol uses Stihl picco 3/8 so I got the same. I'll start with that and see how it goes.
Nothing like hands off cutting. Or is that cutting off…
Might be good to add interrupt beam to each side of carriage as personal and last ditch end stop. I have used the orange coloured little projectors and a driveway type reflector on past projects.
I've considered that too. At the very least I'll have a guard at the end of the bar, attached to the above support bar, which is also use for the auxiliary oiler.
Every log is like a Christmas present!
Looking forward to that!
 
I'm itching to get all the mechanical parts together so I can see how well it really works.

My average logs are ca 25-30cm/10-12" spruce, with a few bigger ones. I bought a 63cm/24" bar, which should be plenty.

I'll let the VFD keep the chain speed constant. Let's say it needs 6A to run full speed with no load and can handle a max of 11A, then I'll vary the feed rate to keep the saw load within the limits.
One advantage of using AC 3-phase motors is that they provide good torque at most RPMs. A gas chainsaw needs very high revs to provide the same cutting power.
In my case the motor runs at 1450RPMs at 50hz.


I'm still looking through my drawers and considering options, but I've almost decided on a 400W permanent magnet AC servo motor that I'll gear down a bit. I'm thinking to start with a larger drive wheel and a wire down the center, but to switch to a chain if it slips.

Logosol uses Stihl picco 3/8 so I got the same. I'll start with that and see how it goes.

I've considered that too. At the very least I'll have a guard at the end of the bar, attached to the above support bar, which is also use for the auxiliary oiler.

Looking forward to that!
Hi
RE feed. I have found that instant reverse is very important for many reasons.
An ideal size of spindle for wire is 1 inch shaft. Most difficult thing with wire wind up is it piles up. 10-20 ft. Is a lot unless endless loop.
Even with endless loop my wire pull set up was problematic, crank by arm allowed hands on feel but wore out shoulder.
Eventually went to a tethered chain down one side of carriage. Chain path was low along carriage rail, up 90 degrees around a 3 inch idle cog, then over a 3 inch cog on a shaft and down to another idle cog, then 90 degrees to continue along rail to an end tether with tension adjust.
Chain best if just bolts, wood rest or something that allows sawdust to drop.
With wire it has to go around an idler or similar and was always getting displaced.
Chain was 100% no problem.
Wire was 1/8 SS aircraft. Did not last.
Just my experience, Hope helpful.
FYI if chain sharp all the time, you can cut 1000 to 2000 LF on one chain and 1/4 a bar. Wait for sawdust you can cut that in 1/2 easily.
I would jig sharpen, low rakes, each tooth sized, touch up 3 times in between by hand. Had but did not need extra oil. Echo used one tank fuel 1/2-2/3 tank oil.
Could keep finger on the middle of the bar 30 sec. after cutting.
 
Hi
RE feed. I have found that instant reverse is very important for many reasons.
An ideal size of spindle for wire is 1 inch shaft. Most difficult thing with wire wind up is it piles up. 10-20 ft. Is a lot unless endless loop.
Even with endless loop my wire pull set up was problematic, crank by arm allowed hands on feel but wore out shoulder.
Eventually went to a tethered chain down one side of carriage. Chain path was low along carriage rail, up 90 degrees around a 3 inch idle cog, then over a 3 inch cog on a shaft and down to another idle cog, then 90 degrees to continue along rail to an end tether with tension adjust.
Chain best if just bolts, wood rest or something that allows sawdust to drop.
With wire it has to go around an idler or similar and was always getting displaced.
Chain was 100% no problem.
Wire was 1/8 SS aircraft. Did not last.
Just my experience, Hope helpful.
FYI if chain sharp all the time, you can cut 1000 to 2000 LF on one chain and 1/4 a bar. Wait for sawdust you can cut that in 1/2 easily.
I would jig sharpen, low rakes, each tooth sized, touch up 3 times in between by hand. Had but did not need extra oil. Echo used one tank fuel 1/2-2/3 tank oil.
Could keep finger on the middle of the bar 30 sec. after cutting.
Might want to rig up a quick hand crank-wire to feel out the VFD response. Increase and decrease bar to log pressure to evaluate cutting. Gotta have good coarse like cookie crumb “chip”. Don’t really get a true chip along grain.
 

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