Motor Building on a Micro Lathe

[LBMiller5]

Hello Everybody!

After I finished my first motor mount, I decided it was time to make an endbell and flux ring to go with it. I was trying to figure out how to make an endbell on the micro lathe and keep it running true. I had some 1.25" by .065 wall thickness steel tubing to make a flux ring. The ID of the tubing was 1.119 inches (28.4mm). This would be perfect for the 23.7mm stators I had. With 2mm thick by 5mm wide magnets, I would end up with an airgap of .12mm. I chucked a piece of the tubing up in my lathe and turned it down to a thickness of 1mm (.039").

I bought a 12" piece of 1.25" 6061-T6 aluminum bar stock, and sawed off a couple slices 1/2" thick (12.7mm). The rotor I designed would have a finished thickness of 10.5mm, and the extra couple millimeters would allow me enough space to square off and clean up the ends. Here is a shot of the endbell blank before I started machining it.

http://innov8tivedesigns.com/rcgroups/RotorBlank.jpg


I started by truing up one face of the aluminum blank.

http://innov8tivedesigns.com/rcgroups/Rotor1.jpg


After I finished truing up the face, I drilled a 2.5mm hole through the center. I would eventually open this hole up to a press fit for a 3mm motor shaft, but that would wait until later in the process.

http://innov8tivedesigns.com/rcgroups/Rotor2.jpg


After I finished drilling the center hole, the part looked like this.

http://innov8tivedesigns.com/rcgroups/Rotor3.jpg


After the hole was drilled I spun the part around in the lathe chuck and cleaned up the other side, and turned down the thickness of the part to the finish dimension of 10.5mm. The center boss on the back side of the endbell is 2mm tall, and the overlap on the edges where the flux ring will press on is 3.5mm. Because of this, I turned down a recess on the back side of the endbell 1.5mm deep (3.5mm-2mm). Then I started cutting down the rest of the inside to a depth of 3.5mm. The finished center boss will be 6mm in diameter. Here is a photo of the cutting process about halfway done.

http://innov8tivedesigns.com/rcgroups/Rotor4.jpg


This is actually the second attempt at the endbell. On my first try I pressed the shaft in after I trued up the ends, before I did any machining. About halfway through the machining I realized that I could not get the angle I needed on my cutting tool because the shaft was in the way. (DOH!) So I ended up scrapping that one and started over. I will be able to finish it later, but I will need to custom grind a cutting tool to reach around the corner. Here is the endbell Just about finished on the back side.

http://innov8tivedesigns.com/rcgroups/Rotor5.jpg


After I finished the inner part of the of the machining I cut the recess on the outer edge where the flux ring would press on. This cut would be 3.5mm long and a little over 2mm deep. The finished dimention was to be 28.5mm to give me .1mm of press fit with the ID of the flux ring. Here is a shot of the flux ring recess being cut. Again, I left this one about .2mm oversize to allow for finish maching later.

http://innov8tivedesigns.com/rcgroups/Rotor6.jpg

After I finished machining the flux ring groove, I drilled the center hole up to the finished size. I was trying to figure out how to drill a hole that would allow me just enough press to get a good interference fit between the shaft and the endbell. They make special drill bits that are cut .001" undersize or oversize for just such an application as this, but I did not have any, nor did I want to wait a week to order one. I started wondering if there was another bit that would work. 3mm is equal to 0.118 inches, so I checked in my number drill bit set and discovered that a #32 is 0.1165 inches. This would give .0015" of press. A little more than I would like, but close enough. I drilled the #32 hole down the center and tried the fit of the shaft. It seemed a little too tight, so I ran the drill down the hole again, but this time I applied a little pressure to the side of the bit with my finger as it went through the hole. This was enough to open the hole a tiny bit and allow the right amount of interference for a good press fit. Now I was ready to press in the shaft. Here is what it looked like at this point.

http://innov8tivedesigns.com/rcgroups/Rotor7.jpg


The shaft I used was a hardened 3mm shaft from a CD-ROM drive. These shafts are used to support the slide mechanism for the laser assembly, and are perfect for motor shafts. They are so hard that they can withstand the forces applied when hammering in the shaft without bending. In order to press in the shaft I used a 3/8" drive socket that was the same size as the endbell. In this case it was a Craftsman 15/16" socket. They have a nice finished back side that is perfectly flat, and as the shaft is hammered in, it goes through the center opening in the socket.

http://innov8tivedesigns.com/rcgroups/Rotor8.jpg


I put a drop of oil on the end of the shaft and started hammering it in. It was a perfect fit, and moved in about 1/8" per whack of the hammer. I drove it in until there was about 3/4" protruding from the other side. After I was done hammering it in it looked like this.

http://innov8tivedesigns.com/rcgroups/Rotor9.jpg


Now here is the reason I left the previous cuts a little oversize. Now that the shaft is installed, I can chuck the rotor into the lathe by the shaft. Now when I make all subsequent cuts with the lathe, they will be referenced to the center shaft, and the endbell will run perfectly true with no wobble or run-out. Here is the shaft chucked into the lathe. At this point I will finish up the flux ring recess to the final dimension.

http://innov8tivedesigns.com/rcgroups/Rotor10.jpg


Here is the endbell with the finished cut on the flux ring recess.

http://innov8tivedesigns.com/rcgroups/Rotor11.jpg


Since I only had a 3mm shaft holding the endbell into the lathe, I was concerned about the endbell pushing away from the cutting tool in the lathe. What I needed was a live center to support the other end of the shaft to prevent deflection as I cut the endbell. Then I came across a great idea. I put a 3 x 6mm ball bearing on the end of the shaft.

http://innov8tivedesigns.com/rcgroups/Rotor12.jpg


Then I pushed the bearing into the drill chuck and tightened it up just hand tight so it would not damage the outer bearing race. This would allow the shaft to spin freely, and would keep the shaft from deflecting when I applied pressure with cutting tool.

http://innov8tivedesigns.com/rcgroups/Rotor13.jpg


In order to show the next part better, I colored the outer part of the endbell with a permanent black marker. This would provide better contrast for the next photos.

http://innov8tivedesigns.com/rcgroups/Rotor15.jpg


The great part about turning the endbell with respect to the shaft is that is corrects for any irregularities in the bar stock. No matter how hard they try, the manufacturers cannot make a piece of bar stock that is perfectly round. In addition to this, if the shaft hole is not drilled in the perfect center of the endbell, the endbell will have a few thousandths of wobble. Here is the endbell part way through the cutting process. At this point I have taken off about .002" off the diameter, and you can see how part of the endbell has not been touched by the cutting tool yet.

http://innov8tivedesigns.com/rcgroups/Rotor16.jpg


The bottom part of the endbell has not been touched yet, while to top part is nice and shiny. I continued cutting the endbell down to the finished outside diameter of 30.5mm. After that, I spun the endbell around so I could cut the front side if the endbell. Here is what it looked like at this point.

http://innov8tivedesigns.com/rcgroups/Rotor19a.jpg


Next I would need to cut down the front side of the endbell. The front support will be 10mm in diameter and 5mm thick. I drew on the outside of the endbell with a magic marker again so I could mark the depth of my next cut. I set my calipers to 5mm and scribed a line on the endbell so I knew how far to cut.

http://innov8tivedesigns.com/rcgroups/Rotor19.jpg


Next I started cutting down the front of the endbell. Here is the front cut about 1/3 done. I cut it to about a 4.8mm depth so I could clean it up later after the rest of the cutting was done.

http://innov8tivedesigns.com/rcgroups/Rotor20.jpg


Here is the endbell about 2/3 done.

http://innov8tivedesigns.com/rcgroups/Rotor21.jpg


After I finished the cut, I cleaned up the face of endbell and de-burred all the edges. Here is a shot of the finished rotor and shaft assembly sitting on the CAD drawing that shows the dimensions.

http://innov8tivedesigns.com/rcgroups/Rotor22.jpg


Here is a shot of the before and after showing the raw materials and the finished part.

http://innov8tivedesigns.com/rcgroups/Rotor23.jpg


Here is a group shot of the motor mount I made last week with the finished endbell and the flux ring I turned down.

http://innov8tivedesigns.com/rcgroups/Rotor24.jpg


Here is another shot of the parts at an angle to show the front.

http://innov8tivedesigns.com/rcgroups/Rotor25.jpg

At this point I still need to drill 6 cooling holes into the face of the endbell and press the flux ring onto the endbell. I will take the parts into work and use the drill press and the big bench vice to finish this motor. Of course I need to wind a stator and glue in the magnets to complete everything. I will post an update when this is finished.

The stator I intend on using will be 23.7mm in diameter and 12mm thick. It has 12 poles, and I will probably use 14 magnets in the flux ring, so it should be a real stump-puller!

(LATE ADDITION) I just realised that I was confusing this motor with another one I am building. The stator in this motor will be 23.7mm, but it is a 9-pole style, and I will be using 12 magnets in it.

The other motors have a 12-pole stator that is 27.5mm in diameter and 9mm thick. The center hole in these is 8.00mm so they fit the new GBx mount perfectly. As soon as the site is back up un line at the end of the week, I will order a couple more mounts!

Well enough for now.

[Felix]

Great post. Thanks for sharing. Its good to see how it done.

Felix

[swatson144]

Hello Lucien,

I just posted 2 of my 12arm motors both delta and wye, in the data base. one is an 18t 25x10mm 14 pole, and the other is a 16t 25x12mm 10 pole. Both are pretty lame on 2 cells (unless one wants to turn a 14-16" folder or a lawn mower blade). as soon as I get the 3 cell packs I'll include the data. They are #70-73. I just thought the info might help while you are in planning stage.

[Felix]

After I finished my first motor mount, I decided it was time to make an endbell and flux ring to go with it.

Is this something that could be done on a machine as small as a Sherline or Taig?

How long would it take a novice to learn to turn out something servicable?

Any ideas on how I could sneak a lathe past my wife? Once it was in the garage, I could tell her that we've had it for years. Unfortunately, she's always home when the UPS truck arrives. :wink:

Felix

[LBMiller5]

Felix,

The lathe I am using is a Unimat model. It is pretty small! Here is a photo of the lathe:

http://innov8tivedesigns.com/rcgroups/MiniLathe.jpg


To give you and idea of scale, the silver base on the lathe is a 16" long piece of 2x6 framing lumber. The distance from the face of the chuck to the tailstock is only 5 inches. The max diameter stock this thing will hold over the bed is about 3 inches, and the max over the cross feed is about 1-1/2" The parts I made in the photos above are really pushing the limits of this tiny lathe. It only has about a 1/20 HP motor, so you cannot take very big cuts. It has 6 speeds that you can adjust by changing the belts on the pulleys at the far left of the photo. The "Belts" are just 3/16" thick O-Rings of various sizes, so they wont take a lot of torque without slipping. I generally run the lathe at it's slowest speed, which is somewhere around 450-500 RPM when cutting.

Since the lathe is made in Austria, the lead screws in it are metric, and each full turn on the crank moves the tool 1mm. Each crank has 20 divisions marked on it, so you can easily see movements as small as 0.05mm, which is equal to .002". So on the scale, each half step is equal to 1/1000 of an inch.

I bought a set of C-2 carbide tipped cutting bits from McMaster-Carr. I picked up about 8 different styles for around $3.50 each. These are good for cutting aluminum & mild steel. When cutting 6061-T6 aluminum, the most I can take off per pass, without dragging the motor down, is around 2 tick marks or .004 inches. When cutting 4130 steel for flux rings, the most I can cut per pass is about 1/2 a tick or .001 inches. This makes the cutting process rather tedious! A larger lathe would allow me to take off 10 times as much material per pass and really speed up the process!

Looking at the 3 parts above in the last photo, I had about 5 hours of time making the mount, 3 hours cutting the flux ring, and a little over 6 hours making the endbell-shaft unit! That is almost 15 hours of total time! A larger lathe would cut the total time down to 2-3 hours. This is a hobby after all, and if you are having fun, it does not matter how long it takes you, but it would be great to have 5 motors after investing 15 hours of time instead of just 1!

This is about the smallest lathe you can use to make motor parts, and you can find them on eBay for about $300. Harbor Freight has a couple mini-lathes available on their website. This first one is a 7" x 10" unit that weighs 89 pounds, and sells for $369.99. The size of lathes is usually represented by 2 numbers the first number, called the "Swing over bed", refers to the maximum diameter material the lathe will handle over the support rails. The second number, called the "Distance between centers", refers to the longest length of material the lathe will hold with the tailstock in place. Another inportant number is the "Swing over saddle" which refers to the largest diameter material that will fit over the cross feed table. This little Harbor Freight lathe has a swing over saddle of 3.9 inches. Here is a link to the lathe on the Harbor Freight website:

http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=33684

Here is a second mini-lathe. This one is is an 8" x 12" size with a swing over saddle of 4.5 inches. This one is quite a bit beefier that the first, and as a result weighs 3 times as much at 260 pounds! It also cost a bit more at $529.99. Here is a link to this lathe:

http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=44859

Either of these lathes would be great for making our little motors. If you want additional machining ability, they also carry a few different 3-in-1 machines. These machines combine a lathe, drill press, and milling machine into one table top unit that would allow you to make any part you wanted. Harbor Freight carries 3 such machines. The first one sells for $409.99, and is based on a 5" x 7" lathe. Here is a link to that one:

http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=39743

The next one is based on a 16" x 16" lathe, weighs 332 pounds, and sells for $699.99. Here is a link to that one:

http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=46199

Their largest one is based on a 17" x 31" lathe, weighs 640 pounds, and sells for $1299.99. Here is the link to that one:

http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=44142

There are other companies that make these type of 3-in-1 machines. shopsmith.com and shoptask.com both have similar units. They are of a higher quality, but they also cost about $3000 each.

If I was getting one for Home, I would probably go with the $699.99 unit from Harbor Freight. It would make any part I could possibly need for any motor I would ever come up with, and still be small enough that 2-3 people could move it.

Well that covers most of the stuff I know of. Does anybody out there have one of these machines that can give us a report on?

Till next time...........

Lucien

[swatson144]

I got the harbor fright 7x10 a month or so ago. I have a history with machines in the navy, real ones, so I have a fair idea of what is going on. I was actually pretty impressed with the machine. It was on sale for $259 I think and just followed me home.

These machines had a lot of problems early on (they have been around in one form or color for about 10yrs). The maufacturer has addressed a lot of the issues in the last couple of years. Now they are pretty decent.

I am space restricted in a 1.5 car garage so I needed something I can move by myself. I can't imagine a better machine that would do that. Ok well there are some rolex precision machines that are about the same size and start at 5k$

The tool post is functional but not convient nor height adjustable, so pretty much until you replace it you are parting with a hack saw. I replaced it with a cheap QC from ENCO for about 40$ Now I can adjust the height for a parting tool. Parting is about all I do with that QC, as Aloris it aint. kinda adds a whole new meaning to "quick change" as I just quick change the tool post. The original is stocked with a brace of shimmed to proper proper height AL5 AR5 D5 etc and does fine. When I need an oddball it goes in one of the 3 QC tool holders.

The drill chuck harbour fright sales for 10$ dollars is OK. No matter what you buy it will hang out about an inch before it gets knocked out . Easy fix either cut an inch off the #2 taper or do like I did and bore a hole for the knock out pin to recess into and knock the drill chuck out of the tail stock in the final 1/8" of retracting the quill.

The assembly of mine was pretty impressive. I was expecting the gibs to be sloppy loose and just put in place but mine was ready to go right out of the box, or atleast good enough for starts.

Google mini lathe and you'll find info on all it's warts and goods. There are several web pages dedicated to them.

Learning these machines is a snap. There is no cross/compound power feed to get you in trouble. A person could make dummy motor parts out of iron/copper pipe and have the required skills to make a motor pretty quick. Like cut two pieces and bore one, make a press fit endbell from the other.

[Felix]

I got the harbor fright 7x10 a month or so ago. .

The lathe I am using is a Unimat model. .

Thanks to both of you for those posts. I'll keep an eye on the Harbor Freight sales. Everything there seems to go on sale several times a year. I just picked up 5 of their multimeters on sale for 2.99 each. While they are not high end quality, they are cheap enough to permantly build into test stands, etc.

I ordered a couple of books from Amazon, "Tabletop Machining" and "The Home Machinist's Handbook". Even if I don't wind up buying a lathe, I'd like to understand what you guys are talking about. (Besides, I've got extra cash this week since Steve won't let us buy motor parts. My wife thanks you Steve :wink: )

Felix

[swatson144]

In the mean time keep an eye on your local forsales. You may get lucky!
You bought books...hmm sounds like you need to clear off space on a workbench :P

[teamsme]

Can you send me those cad drawings, cause i want my friend to turn me a motor.

[Malt_master]

Love the pics and your article.
Question: What type/shape of bit did you use to bore and keep the/get the inside boss?

Like to duplicate your works..
Thanks.. malt

[LBMiller5]

I used 3 different bits. They are all Carbide tipped on 1/4" square shanks. The first one was a pointed triangular bit. I started in the middle part of the recess and worked side to side as I went deeper into the cut. I stopped when I was about .010 shy of my final dimension.

Next I used the bit shown in the 5th photo up from the bottom up above. I mounted the bit so it pointed straight into the cut and worked towards the outside of the part. I had to grind the outside bottom corner off this bit to allow for the curvature of the part.

Finally I used the mirror image of that cutter to do the inside cut around the central hub.

After I had the cut roughed in, I went back and made a final cut with each of the last 2 bits, taking off a couple thousandths. I started at the outside edge, went in to the back of the recess, and then moved in towards the hub until I was a little past center. Then I changed bits, trimmed the outer edge of the hub, and then came back to meet the earlier cut. When I was done, I used a green Scotchbrite pad to give it a satin finish.

Thats about it! Hope that helps.

Lucien

[BlazerB52]

If you guy's need bits and tools for your lathes.
A couple places I buy bits and tools for my mini lathe.
And are priced low.

www.grizzly.com
www.victornet.com
www.use-enco.com

38pc cutter set for $29.95!!! Page 18 bottom corner.

http://www.use-enco.com/CGI/INPAGE?PMPAGE=/Specials/brochures.html&catalog_name=january2007&rfx_page=1

[olmod]

Its my opinion that carbide cutters tear the metal of rather than cut it on small lathes,you cant beat a good quality HSS hand shapened and dressed with a diamond lap or an Arkinsaw stone, with the cutting edge presented to the work piece at the right angle,with the feed rate right you will get the best possible finish and with a cutting fluid even better.saves time later

[ScubaSteve]

Sigh if i wasn't in the middle of a move I'd really consider setting up a little lathe in the garage... :/