Direct Drive Shaper Motors
A woodworker gathers information for designing a custom-made shaper for finish machining of door edges. August 30, 2010
Question
I have several custom woodworking machines I would like to have produced. I am interested in direct drive saw motors for their simplicity in design. Three of the machines involve insert tooling shaper cutters. I am imagining an aluminum body of about eight inches in diameter. These would be similar to the Leitz Proficut or LRH Magic molder.
Does anybody see a problem with mounting a shaper cutterhead directly to a saw arbor such as this? (The amount of material being removed would not exceed 3 X 25 mm). Is there some inherent advantage to pulleys and V-belts or would direct drive do the job?
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I also have a question about measuring rim speed. The tooling manufacturers can recommend maximum rim speed for the tool. The electricians can produce variable speed RPM. How would you go about calculating or measuring rim speed? Would this involve something like a timing light for an automobile distributor or is this a simple formula of motor RPM x tooling diameter?
Forum Responses
(Cabinetmaking Forum)
From contributor Y:
Diameter x 3.17 X RPM = rim speed.
6" diameter at 1,000 RPM's =
19,000 inches per minute
1,140,000 inches per hour
95,000 feet per hour
18 miles per hour
26 feet per hour
From contributor D:
Typically belts are used for one of two reasons, increase torque or increase speed. I direct drive is nice if you can get the speed. You can use a vfd to control that speed. The above formula is almost correct except the number is 3.14 (pi). What you are looking for is tip speed in feet per minute so the formula is dia in inches X 3.14 X RPM divided by 12. A 6" tool at 1,000 rpm will have a tip speed of 1,570 fpm.
From contributor B:
Mounting the cutters directly is really going to beat up the motor bearings.
From contributor D:
You'd have to use something similar to a CNC router spindle.
From the original questioner:
I am curious about the stress on motor bearings. Is this not the kind of saw motor you regularly see on CNC machines?
Contributor D - What do you mean by "use something similar to a router spindle". What does this accomplish?
From contributor D:
A router spindle would have the HP, the RPM and the bearings to handle the side load.
From the original questioner:
Is the router spindle something akin (footprint wise) to this WEG motor? It's a self contained spindle and motor, right?
From contributor D:
A router spindle would likely require custom mounting. Check out cnczone for more ideas. There are lots of smart guys in the DIY CNC router area who could help you pick a spindle and vfd.
From the original questioner:
VFD is variable feed drive?
From contributor A:
The quill contains large diameter bearings for absorbing the forces produced by spinning large diameter heavy cutters at high speeds. The motor bearings themselves cannot handle these loads. By the time you get to the bottom bearing of the quill there is essentially no bending force. The motor simply provides turning motion to easy spinning shafts.
From the original questioner:
Thanks Contributor A, that makes sense. Dropout: I checked out the CNC Zone and found a really great article about CNC machine basics. This is aimed at the person who wants to build their own machine but is probably a great primer for someone who is just contemplating purchasing one.
From contributor E:
To the original questioner: in your search for motors, have you come across any that have arbors long enough to hold wider tooling then a saw blade? When I went to the WEG site I didn't see anything like that being offered. Just curious, as I too would like to make a nice simple machine to notch the back of a drawer box without having to spend the 6-7K to buy one off the shelf.
From contributor R:
You will not get a very good shaper from a motor. Most of the reasonable shapers have a certain amount of preload on the bearings and the larger production shapers use ABEC 7 bearings on top of that. Since most motors have no preload at all with a spring washer controlling the end play, you will have your cutter floating up and down axially as much as a 1/16". The lack of preload will let the radial runout be as much as .002 or more
If you want to see how to make a shaper, take a look at some of the better shapers like Delta and
Powermatic in the heavy duty class and then look at the Moak, Northfield, etc. in the Production class.
Just because you can spin a motor or a shaft at 6000-10,000 RPM doesn't mean that you have the beginnings of a shaper or moulder. It means that you just have a motor or a shaft spinning fast.
The Delta and some of the Powermatic shaper bearing assemblies have a bearing endplay spec of .0010 to .0015. If you go outside those limits the bearings will either overheat or the finish will suffer. One fellow did not believe me when I told him this. He put in new bearings and ran them anyway without taking the preload into consideration. The grease in the bearings nearly caught fire. As far as V-belts are concerned, they have advantages and disadvantages. It all depends on your design criteria.
As abundant used shapers are, I see no reason to make one. The last two shapers I bought cost me $250.00 each. They required a bit a sweat equity before them could be put into service, but both were up and running in about three days.
From contributor R:
You need to look at a multi head moulding machine to really understand the challenges of what you are doing. Like someone else said just having a motor or shaft spinning at the correct speed will not make a moulding machine, or profiling machine, or whatever you are trying to do.
If you look at all the iron that is used in a simple shaper you will start to understand what I mean. Then look at the chassis on a multi head moulder and the feed system. To have an open end spindle like that (even if it is only 3") requires a seriously stable and sturdy mount for the bearing blocks. Also the deflection cannot only be measured relative to the spindle. The most stout spindle on the market with perfect bearings and .0005 runout will cut wood like a lawnmower if there deflection in the chassis between the spindle mounts and the feed system or table.
If this is for rough milling then welding up plate and angle will be fine, but based on the tooling you are talking about using I suspect you are going for a nice finish. This is not easy to engineer, there is a reason we buy $50,000 moulding machines.
From contributor T:
Thanks to this thread I am re-thinking how to get the shaper tooling to rotate. I am not, however, abandoning the initial premise for my machine. What I am trying to accomplish is something similar to a radial arm saw but with the tooling at 90º orientation to your typical radial arm saw. My goal is change how we trim
cabinet doors to final dimension. The current process is to saw them with a slide table saw then edges and the saw marks. The edge sander is probably the only piece of equipment that we own which depends on skill to operate. There's a lot of judgment and finesse involved. Not unlike the acquired skill of shooting pool.
Different lengths of board require different approaches. Different materials or desired outcomes require different approaches. The age of the belt is influential. We currently get a beautiful machined edge on the stick pattern using insert tooling. I'm thinking we could accomplish this on the edge of the board as well and probably accomplish it with substantially less skill and experience. Hence my search for a way to spin the tooling.
From contributor E:
Here's something to think about. My understanding from reading your posts is that most of your doors are inset to begin with. That necessitates precision, and I'm assuming a square edge. When I took a tour of the Walzcraft plant last year I got a chance to see how they do things, and to my amazement I saw them putting doors on a big Komo CNC to just run edge profiles. Now I don't know if every door gets that treatment, because I sure didn't see cart loads of doors waiting to be profiled, but they were doing it to some of them.
The reason I mention this is that maybe a small CNC is just the ticket for you. Depending on what you want it to do will determine the size and the ruggedness of the machine. If it was just for door trimming, you could find a small light duty model that probably wouldn't break the bank, or a small rail and pod machine that wouldn't take up a lot of room either. If you were just doing full overlay doors, I would say build them an 1/8" oversize and set the shaper up like a jointer and trim them like that.
From contributor R:
If all you want to do is clean up the edge of a door, I would find a old Delta or
Powermatic shaper, fix it up, put a 3/4" or 1" solid spindle on it and mount an insert style straight head on it (a la shelix), add some guides and run the doors through. Imagine a jointer with a short shelix cutterhead operating in the vertical plane instead of the horizontal. Set it up with a stockfeeder and it will almost do it all by itself. I believe that unless you are going to use a custom motor with some sort of controlled preloading on the bearings, the likelihood of success is very nil.
In addition, I sincerely doubt you would get an acceptable finish from any shaper that does not have some way of controlling the play present in ball bearings. The cheaper imported shapers have no bearing play compensation in the spindle which is one of the reasons why they are not expensive.
