Shop-Built Custom Shapers

Advice on motor and pulley sizing for a dedicated-purpose shop-built shaper, plus a discussion of the alternatives to making a special-purpose tool. March 3, 2009

I am trying to design some custom shapers for dedicated milling operations. These are going to be similar to a router table but with 1 1/4 inch arbors. The cutterheads will be set up with insert tooling and the diameter of each individual tool will probably range from 3 to 5 inches.

I need some help with calculating pulley sizes for both the arbor and the motor. If, for example, you had a 3450 rpm motor and you wanted a 6000 rpm rim speed at the cutter, what would the pulley size be on the arbor? I'm guessing that different cutterhead diameters might have some bearing on this, but this kind of math is above my pay grade so I am just guessing. Would this be the kind of thing you might use a rheostat on to produce a variable speed motor?

Forum Responses
(Cabinetmaking Forum)
From contributor K:
You want pulley diameters that have a ratio of 1.739 to 1. Divide the spindle speed you want by the motor speed: 6000/3450 =1.739 or a ratio of 1 motor rpm to 1.739 spindle rpm. So, what you now do is choose the smallest motor pulley you can put on the shaft, determine its circumference, then multiply by 1.739 and that gives you the circumference of the spindle pulley. Do the math from that circumference to determine the diameter of the spindle pulley.

The formula for circumference is: diameter x 3.1416 (pi) = circumference
Formula for diameter: Circumference/3.1416(pi) = diameter

From contributor K:
Yes, different diameter heads must run at certain speeds. These are what I know to be the speeds:
max outside diameter of cutter

4" = 10,000 rpm
6" = 7,000 rpm
7" = 6,000 rpm
8.5" = 4,500 rpm

From the original questioner:
Thanks for the math lesson. I have heard that 1750 rpm motors run slower, but with more torque. I wonder if gearing up pulley sizes on a 1750 motor would give you the speed you want but with more power to the cut?

From contributor J:
What is your budget for these? Are you starting from scratch or modifying an existing small shaper? Sounds like a mini Weaver setup. An inverter would be ideal for variable speed control and would also provide motor braking and soft start. I have done pulley changes to get needed speeds, but later wished that I had a more flexible system when my needs changed.

I recently decided to reclaim floor space by shifting my philosophy on shapers. I used to have dedicated setups with stacked tooling (and digital height gauges) for cutters using the same fence setting. This worked very well and made for very fast transitions. But 7 shapers ate up a lot of floor space. I am in the process of redesigning the process around 2 higher quality shapers. They take up less floor space, are very fast to set up, have ISO router style quick-change spindles, and give a better finish. Of course, we use batch production, so this works well for us. The other upside is that we now have room to grow a little more in our low overhead space. I just wish that I had started this 6 months ago so that it was easier to sell off the old shapers!

From contributor L:
I've been down the route the questioner is proposing and found that I was better off buying ready made solutions. There are lots of used decent shapers on the market for relatively cheap. And when you change your system, they are easy to resell. Simple locating jigs can be made to relocate a fence really quickly by dropping the jig into the miter slot and pulling the fence up to it. We also have a digital height gauge for quickly setting tool height. We operate on a JIT basis with dedicated shapers for simple operations, both to save setup time and employee errors. This only works if you standardize your processes. I also like the high dollar CNC shapers with HSK tooling... Donít have any yet. In a larger shop the dedicated shapers can be put next to the conveyors in the best flow positions. We use a few stack head setups with drop on fences or auxiliary tables to compensate for tool diameters or location of a groove. These allow quick changes without much chance of operator error. Almost all of the shapers have power feeds. One even has two feeds, to run parts vertically or horizontally on a lock miter head. Setting up a lock miter shaper and needing to change a feed takes way too much time to have to do from scratch for JIT production. Custom commercial shop, no kitchens.

From contributor K:
I don't know anything about the power transfer issues. I would contact a motor shop to answer that question.

From contributor G:
Contributor K, I believe that you need to divide, not multiply, or else start at the spindle side and multiply to get the motor pulley. If you want the spindle to turn faster than the motor shaft, then the small pulley goes on the spindle and the large one on the motor.

From contributor C:
Like contributors L and J, Iíve been down the dedicated and shop built fixture shaper route and would never do that again. Everything they said plus it keeps your shop from being flexible, especially in these times. Quality is an issue as well. Once you run a quality heavy spindle shaper with well balanced insert tools, you will never go back to less.

After getting rid of our dedicated machines, we ran with only one numeric Martin shaper for a few years, then added another numeric shaper for end coping and tenoning. Now we are in the process of setting up a Colombo stackable numeric tenoner for the end cuts. Built with some options tailored for our products.

Tooling is an important factor in this. If you are just starting with tooling, think about diameters, bore sizes and what machines you might eventually upgrade to. Our 18 piece set for windows is made so all the cutting circles for the sticker cuts are the same. Likewise for the cope and tenon heads. These cutters are all on sleeve so the height matches up for everything also. Our door tools built later are the same setup.

With the right tools you could get by without a numeric machine. We do a lot of other stuff, so the numeric control pays off for us.

The Martin has a quick change spindle. Originally I was going to buy a spindle for every cutter but decided changing the cutter is only about 45 seconds longer and pretty much do that. Sometimes we stack 2 or 3 cutters depending on the work. Cutters stacked on sleeve are a good option for setups repeated a lot.

SCM has a simple ISO 40 spindle they use on their small Ten 220 single end tenoner. The machine is nonnumeric, made to be used with constant height and diameter tools. The spindle releases and clamps by air and is very quick to change out single tools on dedicated spindles. There are a lot of options anymore for spindles with all these machines.

From contributor K:
Contributor G, you are correct! I got the ratio backwards. Did I get any of it correct? It's been a while since I needed that formula. Actually, a good motor shop may even have a chart to work off of, so he doesn't even have to do the math.

To the original questioner: Divide the motor speed by the spindle speed to get your ratio of .575, then multiply your spindle circumference by .575 to get the circumference of your motor pulley. Break that down to find the motor pulley diameter from the original circumference formula.

Did I get this correct?

From contributor G:
Yes sir, you have it perfectly correct.

From contributor B:
So why is it that mass-produced products are so often built with custom-made machinery? Those machines that spit out Oscar Meyer wieners didn't come from Stiles!

We build all kinds of custom jigs for our products. Why not a custom machine? We crab power feeders onto anything, devise plywood sleds and use those little red clamps all over the place. Bolting a router to a tabletop isn't that different from sticking a spindle attached to a motor through a bigger tabletop.

Obviously there should be a cost-benefit analysis done for investing in a custom made or single-use machine. At some point in volume, a custom machine makes all kinds of sense. Determining that point is probably the difficult part.

From contributor T:
A good reference for proper cutting feeds, speeds, and configurations is a book called "Chisels on a Wheel" by Jim Effner. It has been out of print for some time now, but is being offered in a reproduction at This book is quite technical in regards to woodworking cutting tool performance and setup. It is a good reference for anyone wanting to build their own machinery for woodworking.

From the original questioner:
Contributor C, I think if I had a product line as varied as yours, the very best way to produce it would be with extremely flexible machines like you have. My product line, however, is pretty well defined and for a variety of reasons would benefit from more specific, dedicated work stations. There is a lot of opportunity still for innovating woodworking processes, particularly as they apply to bucket brigade work cells. Where a machine lives in the shop is often dictated more by how big it is than where it logically fits in the work flow.

Size is related to complexity. A typical shaper has the ability to change belt speeds, spindle heights and fence positions. Dust collection ports tend to come in from the back rather than the top, also increasing footprint. When everything is said and done it takes 16 square feet just to get 5 inches of cope.

I think my first shaper would be a real pain to produce, but the 3rd, 4th and 5th would be a breeze because I would already know which parts to order and which machine shops to hire for the things that could not be purchased off the shelf. Besides, if I was a real businessman I would probably own a laundromat.

From contributor C:
I think dedicated machines work for shops that have the space and build the same product daily. I would love to only sell what I build, but in my local market I have to be flexible to survive. Even more so now.

I still question the idea of building your own machines. Are you trying to save money or do you think you can build a better mousetrap?

When we had dedicated shapers they were clustered in groups of 4 with the DC pipes going straight up. I didnít use any of the stock fences and had shop built hoods and Weaver systems on most of them. I think the space for 4 machines was not any more than 16 sq. ft.

From contributor A:
What is your theoretical budget for each shaper? How many shapers?

Weaver Sales wants $750 for a spindle setup. Throw a $350 motor at it. You are talking $1500 in parts, no labor. You could buy a bunch of cheap Taiwanese for less than that and replace them every 10 years (they might last you 25).

From the original questioner
My interest in custom shaper operations is not to save money. We are trying to develop a work flow that approaches each product family in a bucket brigade type fashion. Optimally this will involve a series of contiguous work stations with a small buffer between each work station. The buffer will serve as a kanban for GO or NO GO. If the buffer downstream from you is full, go help the fellow downstream. If you find yourself waiting for product, then go help the guy in the previous process.

This is essentially a self managing line that can be balanced in order to make everything flow continuously. Think of it as one piece flow one product family at a time.

Ergonomics are very significant with fast paced work. Having more control over the footprint and configuration of each work station is more important than what the actual savings might be from buying an off-the-shelf shaper.

There are additional benefits from learning something about manufacturing machines. After you have a couple of them built, you can easily amortize the effort over several more. I'll sell ten of these machines to some of you on this forum (though some of you will have to pay more than others).

For the most part this stuff will be put together with off-the-shelf elements. Some of it will involve a DXF file and a waterjet cutter and some of it will just involve a local machinist. Other than the planning, most of the R&D is outsourced already.

The goal is to be able to staff a company with similar demographics to those people you might find working in a Starbucks. For the most part these people score very high good citizenship characteristics. While they are a migratory group they are also quite educated and easy to train. These people are probably generating profit quicker than most similar applicants in the woodworking industry.

I have about a dozen machines in my head right now and if any of those reach fruition I suspect they will beget a dozen more. Most of these machines do not exist today. The ones that do are not real conducive to small footprint or small budget.

A great example would be a vertical panel saw for drawer boxes. I need something to crosscut a 12 inch board and I would like it to fit within the district we build drawer boxes so as to minimize transport costs or scheduling conflicts.

A lot of the motivation for this concept comes from Taichi Ohno's memoirs. For him the perfect work cell could be run by one person if demand was low, but could also accommodate four people if demand was high. The work flow I envision could do just that. This is where our flexibility will come from.

Whenever somebody tells me that it doesn't make sense for a woodworker to design machinery, I am reminded of the founder of Tigerstop. He used to be cabinetmaker in Oregon. He saw a need and filled it.