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Old May 07, 2010, 07:33 PM
Jack
USA, ME, Ellsworth
Joined May 2008
16,919 Posts
Mini-HowTo
Making and Replacing a Brushless Motor Shaft

Making and Replacing a Motor Shaft

This shaft was being used with a collet type folding prop yoke/spinner when a nose strike on a rock bent the shaft. It is a 3mm shaft and the motor was a Turborix D2830-800 brushless outrunner.

The bent shaft has been removed from the motor in the first photo. To do that I used a jewlers screwdriver to pry the circlip away from the shaft at the back of the motor. Do that carefully so you don't lose it, some like to do it in a plastic bag but I couldn't find my plastic bag.

Look carefully to see if there is a thrust bearing under the circlip. If so, remove that too or at least keep track of it..

The shaft and magnet housing slid forward and out of the bearings and the motor came apart easily in this case. I put my fingernails in the gap between the magnet housing and the motor base/stator housing and pulled hard enough to defeat the magnets and the shaft and housing just slid right out of the bearings.

There were two small metric socket head Allen head grub screws holding the shaft in the magnet housing, I loosened the grub screws and the shaft slid out. In some cases a few gentle taps with a soft hammer may be needed to get the shaft out of the housing.

In the first photo is the bent shaft and a 3mm shaft removed from a CD-ROM drive.

The circlip groove near the end was the only one being used, the other circlip groove is not needed and will not be duplicated. The second circlip groove is the one that would allow that shaft to be mounted for a "firewall mount" with shaft extending out from the back of the fixed part of the motor.

So we will cut it to length, duplicate the circlip groove near the end, and cut the grub screw flat. I have already marked the cutting point for the length, I will use the longer part on the right for the new shaft.

The tools needed are:

- 3/8" or 1/4" drill motor

- Dremel tool with #409 abrasive cutting disc and #402 arbor (any other Dremel abrasive cutting disc like the fibreglas ones will be too thick and will not work)

- Safety glasses or other eye protection.

Added Note Aug 2014 - I recently found the perfect abrasive disc for cutting Circlip grooves at Harbor Freight and they gave them to free! I got a flyer in the mail with a coupon for free set of "Diamond Coated Rotary Cutting Discs 5 Pc set" and gave them a try. They are thin and very durable. The five pieces set will last me a long time. They cut very nicely, making no sparks but still generating some abrasive dust and debris. And the groove was perfect for a circlip. Free was wonderful of course, the normal prices of $7.99 for a five piece set is cheap enough, but I have also seen them on sale for less, like $4.99 or so.

My cutting setup is seen in the second photo. I use a 3/8" VSR drill motor and have the shaft chucked up with the point of the cut a short distance from the chuck. That drill will lay flat on it's side as seen there, I lay the Dremel tool with a #409 abrasive cutting disc mounted flat on the bench top and the two shafts are parallel to each other and you can hold the drill motor and Dremel tool down solidly as the cut is made.

The third photo shows how the cut will be made by bringing the abrasive disc into contact with the shaft. I have arranged the rotation of the drill motor and the cutter so that the shaft and abrasive disc are rotating in opposite directions at the point of cut. As seen there, from the right, the drill motor and Dremel tool are both turning clockwise so the shaft is coming up and the abrasive disc is cutting down. This also causes the sparks and abrasive residue to be directed down at the bench top and not into your face and eyes.

You only get one set of eyes, take care of them. The #409 discs can shatter if they are jammed or over stressed in use. The fragments are small, light, and not too dangerous but you do need to use some eye protection here.

Start the drill motor at full speed and lock it on run. Start the Dremel tool at full speed and hold it down firmly against the bench top with your right hand. Hold the drill motor down with the left hand. Make sure the shaft being cut and the Dremel tool shaft are parallel.

Slowly slide the Dremel tool towards the shaft and maintain very light contact as the sparks start being seen. There will be little or no pressure needed or to be felt at the point of cut, use jjust enough to produce a steady stream of sparks. If you don't see sparks it it not cutting well. It will take about 15 seconds to complete the cut and the small end will simply fall away.

In the fourth photo I stopped the cut when it was about half way through the shaft. As you can see the kerf of the cut is narrow and there is no evidence of heating or discoloration. That is the way it should always be with abrasive cutting of hardened tool steel like this.

I finished the cut. If I was going to use the shaft with a tip off prop saver I would use the side of the abrasive disc near the edge to grind a rounded or chamfered end on the shaft so that there was a smooth rounded surface on the end of the shaft. That was not needed for this shaft.

In the fifth photo the shaft has been repositioned and the location for cutting the snap ring groove is marked. The cut will be made the same way as the cutoff was, it will only take two or three seconds to cut the groove to depth. Bring the cutting disc in once square to shaft, touch the shaft lightly for a few seconds and it will produce a nice square circlip groove on the shaft.

Slide the circlip over the end of the shaft and make sure it slips into the groove and cannot be moved by applying pressure to it. The circlips can be deformed in removal, using a new one is a good idea. I have carefully straightened them out and used them again though. If they appear to be sprung open too much, you can gently close them a little with a small pliers.

In the sixth photo the circlip is in place and the location for the grub screw flat has been marked on the shaft.

In the seventh photo I have clamped the shaft in a small vise, a locking pliers or small clamp can to used to immobilize it well to grind the flat. The abrasive disc will be brought into light contact with the shaft and moved up and down the shaft a few times to cut the flat. I move it the distance of the blue marking and the point is to just produce a narrow flat for the grub screw to bear on.

In the eighth photo the flat is cut and the shaft is finished and ready to use.

In the last photo the shaft was slid into the bearings and the motor housing slid down the shaft to the position where it wanted to be to centralize itself over the magnets.

Sometimes with snug fitting shafts it is necessary to find the centralized location (maybe even using another looser fitting shaft to do it) and measure the width of gap between the magnet housing and the mount when the magnets are centralized. The gap can be measured with feeler gauges or something like that.

As you can see looking at the grub screw hole, the flat is visible and everything is ready to go back together. Make sure that the circlip is up against the bearing race and the thrust washer (if there was one) is in place beneath it.

Check the gap between the magnet housing and motor base to make sure the magnets are centralized, and put blue Loctite on the grub screw and put it in place. This motor has a second grub screw also, I did not cut a flat for that screw but I also put it back with Loctite on it.

If you buy or have shafts for other motors you can often use the circlip groove and simply cut them to the needed length, ignoring any other grooves or flats that are not needed or used.

Note added 20120711 - If you are using prop saver bands you should use the World's Best bands made from Thera-Band exercise tubing. Full details here:

Prop Savers - Fitting, Using, Testing, & Making Thera-Band Bands - http://www.rcgroups.com/forums/showthread.php?t=1419378

Jack
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Last edited by jackerbes; Aug 24, 2014 at 07:35 AM.
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Old May 08, 2010, 03:56 PM
five by five
sonicj's Avatar
Panama City Bch, FL
Joined Jan 2009
2,074 Posts
nice work!

after cutting a new shaft, i like to bevel the cut end. i just chuck it up in the dremel and work it against a little piece of sand paper. not completely necessary, but it gives the shaft a nice finished look.
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Old May 09, 2010, 06:44 AM
Jack
USA, ME, Ellsworth
Joined May 2008
16,919 Posts
Shortening a Shaft While Still in Motor

The same tools and techniques used above can be used to shorten a shaft without removing it from the motor.

I attach the motor to the side of a block of wood, power it up with an receiver and ESC (some servo testers can be used to it too), and run the motor at a medium speed while I am doing the abrasive cutting.

It is not a good idea to run a motor at full RPM for more than a few seconds without a prop or load on it.

It is a good idea to put a plastic bag with a small hole in it around the block of wood and motor while doing the cutting to keep abrasive particles from getting into the motor.

Jack
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Old May 09, 2010, 03:48 PM
Reduce the drama...
rick.benjamin's Avatar
USA, OR, Damascus
Joined Apr 2004
4,043 Posts
Nice "How To"
Thanks, Jack!
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Old Jun 03, 2010, 02:03 AM
Registered User
Athens, Greece
Joined Apr 2009
165 Posts
Where on earth do you guys find this 3mm shaft? I opened a CD-ROM drive and besides the little motor, I couldn't find this nice long shaft
Thanks,
Thanos
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Old Jun 03, 2010, 04:57 AM
five by five
sonicj's Avatar
Panama City Bch, FL
Joined Jan 2009
2,074 Posts
it is the laser guide rail. some transports have one, some have two.

#2 in attached photo
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Old Jun 03, 2010, 06:12 AM
Registered User
Athens, Greece
Joined Apr 2009
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Thanks a lot sonicj !! Now I know where to look...
Thanos
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Old Jun 03, 2010, 07:01 AM
Jack
USA, ME, Ellsworth
Joined May 2008
16,919 Posts
Sometimes there is more than one shaft in CD/DVD drive. The shaft with the spiral groove that moves the laser projector or moves the tray might be a candidate too. Just ignore the groove and use it. And I think I've also found shafts that were the rails for the CD tray to open and close on that were good.

I also look at the screws that come out and save the 2mm, 2.5mm, and 3mm or so screws as they will work in other places.

For larger shafts 3.175mm, 4mm, and up you can buy the cheap replacement shafts from Hobby King, Head's Up RC, or one of the other supplies and keep them on hand and quickly modify them to work with other motors.

Jack
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Old Jul 14, 2010, 11:09 AM
Registered User
Lawrence, Kansas
Joined Dec 2001
588 Posts
c-clip blues

I have replaced shafts on a couple Hobby King/Turnigy motors and have never manged to get the C-clips off without mangling them. They are the kind that go almost all the way around the shaft and have a little expansion with a hole on each side of the opening of the ring. As I recall, they seemed to be very thin copper, and the grooves in the shafts were so narrow, the hardware store C-clips and E-clips I tried to use as replacements were way too thick. I spent a long time sanding them down to fit. Next time, I'll use your Dremel technique, have one right now that needs a new shaft.

- - Dave
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Old Jul 14, 2010, 11:59 AM
five by five
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Panama City Bch, FL
Joined Jan 2009
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these are super handy! 3mm Grip Rings
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Old Jul 14, 2010, 12:53 PM
Jack
USA, ME, Ellsworth
Joined May 2008
16,919 Posts
C-clip blues:

I spent some years as a machinist and gunsmith and had all the tools to remove virtually any kind of clip. For the most part, the kind you describe with two holes or notches in them are intended to be expanded just enough that they can slide off of the shaft. You'll never get them to clear the shafts diameter.

To remove them without the right tool I hold one end down and use a jewlers screwdriver or exacto knife tip to lift or pry the other end out of the slot and up just far enough that it rests on the shaft. At the point the clip is slightly disported and skewed on the shaft with one end out of the groove. Put a jewelers screwdriver tip under the raised end and twist it back and forth a little and walk it around the clip. With any luck the clip will be above the groove and can slide off of the shaft.

For the "E" type clips, which are intended to be for mounting by being forced down into the groove because you can get at the end of the shaft, you can push on the two slightly exposed tips with a wide flat screwdriver and they will usually back up a little. Then you can put a jewelers screwdriver into one of the two openings and pry it back and off.

I try to have new spares but I will re-flatten, straighten, and "adjust" the size on clips if necessary to reuse one.

The grooves made with the #409 abrasive discs have always worked for me. Those discs are about .025" thick and will cut a nice, square shouldered groove if you use light pressure to make the cut. The depth is more a matter of timing than anything. I like for a clip to rotate easily when it is in the groove. But too deep and it won't stay on of course.

There are some thicker Dremel abrasive discs and flexible discs that will not work as well or even not work at all. The #409 mounted on a #402 arbor is the right combo. With the user wearing eye protection of course.

Jack
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Old Jul 15, 2010, 04:47 PM
Registered User
Lawrence, Kansas
Joined Dec 2001
588 Posts
Thanks for the tips! Yup, the clips I tried to describe are the bottom ones on that Knipex page, the "external" ring. I have a couple different types of Dremel discs, I'll have to make sure I have the right one before making new grooves. Not sure it is worth trying to salvage the original rings on these cheap Chinese motors. They are so thin, they almost seem like thick foil.

Thanks again for all the great information!

- - Dave
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Old Sep 17, 2010, 11:33 AM
Build 'em break 'em fix 'em
chinaclipper63's Avatar
Joined Oct 2009
439 Posts
Tried this last night....

Quote:
Originally Posted by jackerbes View Post
Making and Replacing a Motor Shaft

Jack
I tried this last night, ie cut, reversed and put a groove clip in a spare shaft that I had to fit another engine.

Worked like a champ!

Thank you so much for this helpful and well-done description
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Old Sep 17, 2010, 12:31 PM
Jack
USA, ME, Ellsworth
Joined May 2008
16,919 Posts
Thanks for the thanks guys!

And thanks for the additional links and images and other good info too! I love a helpful thread.

And friends shouldn't let friends have to wait for Hobby King to send them the wrong replacement shaft too! I went through that two times and that was it for me!

Jack
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Old Sep 17, 2010, 02:11 PM
Registered User
Cumbria in the U.K
Joined Jan 2008
1,927 Posts
Thanks for a very informative post and a great way of making a new shaft.
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