New Brushless DC Router Spindle
I have had a project going in the background to create a small, but strong and quiet spindle for small CNC routers. This is my second iteration of the design and I think it is close to what I want.
Frame
I started with an UHMW frame. This frame presses together then uses some hi-lo plastic screws to keep it together. UHMW is very stiff, but cuts well on a simple CNC router. I used a 1/8″ single flute end mill for all cuts. I try to ramp plunges wherever possible to limit the meterial that tries to climb the tool. It can all be cut from a sheet from one side with the exception of the pocket for the motor. This is needed to get enough shaft to come through. This pocket does not need close registration with the other so it is easy to flip it and run that side. The frame is rock solid. It feels like you could drive a car over it.
Spindle
The spindle shank was a key find off eBay. It has a ER11 collet which can handle a little larger then 1/4″ bits and there are plenty of cheap metric and inch collets available. The shank steps down to 8mm. This is great because the step can ride right on the lower bearing and cheap normal and angular contact 8mm bearings are available. I used an angular contact bearing on the bottom, and a normal bearing on the top. The top pulley installs with a spring washer to keep a 8-10 lb pre-load on the bearings to eliminate axial play. The bearings press fit into the end plates. The lower angular contact bearing takes the axial load from hard plunges. The axial bearing I found does not have a good seal on it, so I am a little worried about that. I am looking for a better bearing, but I might make my own seal that would seal to the spandle shaft. I might add a cover for the front and top.
Pulleys
I am currently using MXL belting which is rated for about 20k RPM, but at this diameter and length I think it can go a lot higher. I was planning to use multiple rubber o-rings, but that requires custom pulleys.
Size & Weight
The overall size is rather small at 90mm x 84mm x 82mm and total weight is 0.72 kgs. You mount it by tapping holes into back side. I will have a standard set of holes, but leave room for custom mounts.
Motors
It accepts a variety of motors. You can use univeral motors for small power tools. These will work on AC or DC and are good if you want to run it off 120/220VAC. You can also use RC hobby motors. These are available in brushed and brushless DC. A brushed 12VDC motor is cheap and the you can use a cheap PC power supply. I also test a water cooled brushless DC motor. This is the quietest option, but has the added cost of a speed controller. The motor shown will do over 30k RPM. I need to modify the top to give clearance for the water fittings. It can run for a few minutes before it gets hot, if you don’t load the motor too much. This motor can pull over 550 watts continuously. That is more than 2/3HP. I am hoping a simple PC cooling system will do the cooling.
Speed Control
The speed controller is controlled like a hobby servo. It uses pulses in the range of 1ms to 2ms to set the speed. You can program the controller though the servo interface to determine if you want reverse, etc. I decided to use an Arduino to control the speed. There is a servo library that makes it easy. I have the Arduino reading a pot them setting the speed accordingly. You program the controller by powering it up with the pulse input set to max speed. You then can set a few options like range and direction.
Next Steps
The next step is to find a way to do real world testing with it. I need a water cooling system and something to mount it to. The design will be released as open source.
Thanks for sharing this. I have a similar need and an application for low speed and high torque where the lateral loading is not significant.
I am considering using the same 8mm shaft ER11 collet holder used in your project to replace the 8mm shaft in a large outrunner motor:
http://www.hobbypartz.com/96m608-bigfoot160-5335-245kv.html
It looks like it is long enough and I am hoping for press-fits. I would appreciate your thoughts. Thanks again.
In regards to Robert’s comment: There have been a couple UK hobbyists who have attempted what you are talking about (replacing the motor shaft with the ER11 shaft). They seem to have no problem with the swap out, but they mention making reliefs in the shaft diameter where the bearing are not located so the shaft slides through all the bearing easier… maybe even cooling the shaft in the freezer to reduce it’s size a fraction.
For the design shown above: Are you concerned with debri getting in the motor? I would think mounting the motor up top might be better… further away from the work. You wouldn’t want to cover the motor up to prevent chips from entering the motor because it needs the air movement to cool it while its running. Unless you intend to run it at lower RPMs.
This is a really nice idea and well executed. I will be interested to see how it works out. What is your primary material to be cut with this?
I will be making a spindle like it for cutting aluminum.
Adam
The shaft goes on like butter. It is fine. The motor is water cooled so it can be covered. The bearing needs to be watched though. I have a friend testing it. It has a lot of hours on it now. I have not heard about him cutting aluminum yet.
I am looking for a spindle that I can use to get the full potential out of my 425 oz-in stepper motors. Is there anything that I could let run for a while (3-4hrs) and can take some serious lateral forces?