Converting Thickness Planer to CNC

[skibuilder]

I’m betting that this thickness planer mod has been discussed somewhere before on this forum, but I’ve done numerous searches both here and on the web, and haven’t come up with any hits. I have a 20 inch width capacity thickness planer that I would like to convert to CNC. I make snow skis as a hobby and I’d like to use the planer to ‘profile’ the wooden cores for the skis. These cores are about 72 inches long and vary in thickness from about 3/32 at the ends, to 1/2 inch at the center. Up until now, I’ve been using a router bridge set-up, but I’m just about finished with my first CNC router that I’d planned to be taking over the task of profiling. But, I’ve been bitten bad by the CNC bug. I’ve been thinking that a thickness planer would do the job much faster if I could accurately control the variable cutting depth. So, my plan is to remove the current hand wheel depth adjustment on my planer and replace it with a fairly large stepper motor. The G-code should be pretty easy to write because there are only about 6 points along the longitudinal axis of the core where the thickness changes.

Since the planer already has its own in-feed system, the only CNC control I would need would be the depth of cut (I’ll call it the Z axis), so a single axis driver is all that would be necessary… I think. The only part that I’m not too confident about is whether or not the control software (Mach3, most likely) will accept data regarding feed rate (I’ll call this one the X axis) when that data is not input as step and direction (or encoder) data for a stepper (or servo) motor. Basically, the feed rate data would need to be input somewhere into the control software in terms of ‘feet per minute’ or ‘inches per second’. Does anyone have any thoughts, suggestions, or prior experience with this type of software ‘work-around’? Where in the software control panel would I enter this information?

I plan to use an optical sensor (similar to that used to sense when a piece of paper enters a computer printer) to inform the control software when a core blank has been fed into the planer.

Thanks in advance,

Dana

[kenrik]

Originally Posted by skibuilder Since the planer already has its own in-feed system, the only CNC control I would need would be the depth of cut (I’ll call it the Z axis), so a single axis driver is all that would be necessary… I think. The only part that I’m not too confident about is whether or not the control software (Mach3, most likely) will accept data regarding feed rate (I’ll call this one the X axis) when that data is not input as step and direction (or encoder) data for a stepper (or servo) motor. Basically, the feed rate data would need to be input somewhere into the control software in terms of ‘feet per minute’ or ‘inches per second’. Does anyone have any thoughts, suggestions, or prior experience with this type of software ‘work-around’? Where in the software control panel would I enter this information? I plan to use an optical sensor (similar to that used to sense when a piece of paper enters a computer printer) to inform the control software when a core blank has been fed into the planer. Thanks in advance, Dana

Sounds like a very interesting project. Have you figured out how you will control the powered in feed and out feed rollers to follow the variation in the profile Heights as you are feeding the material through the planer ?

[Greolt]

I'm having trouble imagining how you will get the feed rollers and cutter head to move up and down independently.

Greg

[zenbot]

just a thought. you could replace the feed roller motor with a stepper motor. Then you just need to figure out the steps per inch of travel on the surface of the feed rollers. You could completely control the cutting action of the machine this way.

[skibuilder]

Hey guys,

Thanks for the responses. I re-read my original post and can see that I may not have been very clear with my writing. I'll try to elaborate a bit more clearly. The ski cores blanks, before thickness profiling, are a consistent thickness of about 9/16 inch (about 72 inches long and 6 inches wide). After profiling, they are 3/32 thick for about 12 inches at each end and 1/2 inch thick for about 8 inches in the center. There is a consistent taper between the end flats and the center flat.

With my factory-stock thickness planer, I can do a fairly crappy job of profiling the cores just by manually turning the hand crank clockwise and counter-clockwise (raising and lowering the feed rollers and cutter head) at the appropriate points along the length of the core blank (tapers up, then, tapers down). My planer will only allow a 1/8 inch maximum depth of cut, so I have to make about 3 passes for a finished core. If I could control the raising and lowering of the feed rollers and cutter head more accurately, like with a stepper motor driven from some appropriate G-code, I think the planer could do a real fine job of profiling.

Yes, zenbot, I thought about changing the drive motor to a stepper motor, but the present drive motor (a big ol' 5 horse belt driving motor) powers both the (geared together) cutter head and the feed rollers. I'll give it some more thought, though... there may be some way to detach the feed rollers from the gearing system, and then drive the feed rollers with a stepper. Driving the feed with a stepper would just about solve my dilemma... well, maybe not... there's still the task of getting the optical sensor to tell the 'Z-axis' when to initiate the cutting depth values.

I may have to end up building a custom thickness planer that has stepper driven feed rollers on the bottom and floating pressure rollers on top, then a separate stepper positioned overhead cutter-head.

I'd still like to try to get the current planer to work, though. There may be something in the Mach3 software that will allow me to enter the stock machine feed rate speed for the 'x-axis' value.

Thanks again for responding to the thread.

Dana

[Madclicker]

You have 2 axes to control. Why even try to control one without controlling the other?

This is just a simple problem of controlling the feed speed and the height of cut.

Sounds like you just don't want to build the dedicated machine that you know you need to.

[bluejay_ca]

If you can do it by hand then it is at least possible. You are assuming that feed is constant. An input for presence of part entering planer would start program and continue to provide signal for repeated passes.



Personally I'd use a plc to monitor feed rate and a stand alone servo/stepper drive with position inputs. Once the program was finished the planer would open up for the next board.

[Adamj12b]

Could you post some more information about the planer? Maybe some pictures of the drive system and stuff. It certainly sounds possible to accomplish. Also the feed should be the same with a 5Hp motor, That size planer is hard to bog down.

[skibuilder]

Yes, Madclicker, you may be correct regarding the dedicated machine. I spend a lot of time on a hobby skibuilder's forum where a lot of folks are trying to figure out how to get their thickness planers to function reasonably well as profilers. I was just hoping to come up with a planer mod that a number of others, besides myself, could benefit from. I knew that the thickness planer cnc conversion could be a long shot.

Bluejay-ca, could you elaborate a little on what a 'plc' is. Also, what do you mean when you refer to a 'stand alone servo/stepper drive'? Whether I do or don't end up building a dedicated profiling machine, I have a feeling that I could benefit from understanding more about your suggestions. Regarding a modified feed system, it takes an awful lot of force to get a board to feed against the planer's cutting head (even with very sharp blades), so if I did use a servo/stepper to drive the feed system, I'd probably have to incorporate some element of gear reduction. I'm not too concerned about speed at this point. I'd just like to better consistency and accuracy.

Adamj12b, I have a 20 inch Grizzly planer. It's about 20 years old, but still looks just like the model in the current catalog. You are correct in that it does take quite a bit to bog down that big ol' machine. The in-feed rollers have a pretty aggressive bite to them, so the feed rate is pretty reliable. I took the gear housing cover off today, and noted that it is a chain drive. I don't know why I never noticed it before, but the feed speed selector has a "idle' position where the feed rollers don't turn. I don't think that will help me any though, because if the feed rollers aren't turning, I don't think I could feed a piece of wood past them, even if I were to figure out a way to use a stepper or servo to manage the feed aspect.

I'm feeling pretty much split 50/50 right now regarding whether I think the conversion might work vs. needing to build a whole new machine. A new machine would be a pretty hefty project... maybe a bit much for 'hobby' status. So, I'll probably keep dinking with the conversion idea for awhile. Ha, I need another project like I need another hole in my head. I haven't slept much since I discovered cnczone.

Thanks again for the feedback.

Dana

[VWSatOz]

What about a simple copy mill? Place your workpiece on a long base board with a template on one side or both sides set below the cutters lowest point, fit cam follers near to the cutter head and just feed your work through, the cutter head will smoothly feed up & down following the templates, then use twinned-drive down feed screws to adjust the depth of each pass. Sounds such a simple profile why bother with CNC

[skibuilder]

Hi VWSatOZ,

I hadn't heard of a 'copy mill' before reading your post. It perked my interest so I did a google search, but the only thing I could come up with was cnc based copy mills. Do you happen to know of a link that would have a picture of a machine similar to what you describe? From your description, I think that I get the general idea. I'm currently using a router 'bridge' set-up to profile the ski cores. It uses template rails (one on each side of the core) to guides the depth of cut of the router. The router has a 1 1/2 inch 'fly cutter' type bit, so the actual process only takes about 5 minutes, which is fast enough that I can easily live with that part of the process. The main reason for wanting to go to a cnc based machine is that every pair of skis varies a bit in the thickness of one or more areas of the core. Even a 1/32 inch change in thickness in a particular area of the core can significantly change the performance characteristics of the ski, so I might have 30 or 40 basic core profiles that I'd like to be able to draw from. I have tons of templates already and they're kind of a pain to keep track of. It now takes me a good part of a day to make a new set of template rails. If I had a cnc programmable thickness planer, I could draw the profile up in CAD in about 5 minutes, then let the machine cut the profile. I could certainly use my almost finished cnc router to to profile the core blanks, but the cores get so thin (tips and tails) when profiling, that I'd have build a vacuum table to hold them down because the router tends to suck up and destroy them. In my experiments with my planer, it seems to handle the thin sections pretty well (I run them through on a shuttle board).

Thanks for taking the time to share your thoughts.

Dana

[Oldmanandhistoy]

Can you not use an encoder on the feed rollers to monitor position?

John