How to unfix this fan from the shaft of this DC motor? - Page 1
Forum section: electronics / repair

author: saaluc
author_rank: Contributor
timestamp: December 12, 2024, 02:41:58 pm
content: Dear users of EEVblog ForumThe DC motor you can see in the attached pictures, is not working; I connected different voltages (6-24 VDC) to it but it drew no current and did not react at all. I think I have to replace it.But the problem is that it does not come off by just pulling it out. And there is no direct access to the base of the fan, because of the plastic housing.My questions are:1. How these kinds of fans are fixed on the shaft of these kinds of motors? by glue, or by melting, or other methods?2. How can this fan be unfixed from the shaft?

author: Ian.M
author_rank: Super Contributor
timestamp: December 12, 2024, 02:56:59 pm
content: Probably a machine press or shrink fit. Extremely difficult to remove non-destructively and even more difficult to reattach successfully as prying it off often wallows out the hole enough it will spin on the shaft during startup acceleration if you simply push it back on and many glues are no good in a tight fitting plastic/steel interface. Loctite and similar thread and bearing lockers *MUST* *NOT* be used as they degrade many plastics causing microcracking and brittle failure.

author: elektryk
author_rank: Regular Contributor
timestamp: December 12, 2024, 03:13:11 pm
content: Maybe carbon brushes are worn out?It is a bit tricky to replace them but possibile indeed.

author: saaluc
author_rank: Contributor
timestamp: December 12, 2024, 03:32:21 pm
content: Quote from: elektryk on December 12, 2024, 03:13:11 pmExcellent idea!Do you mean by "brushes" the things that I have encircled in red in the attached picture?

author: themadhippy
author_rank: Super Contributor
timestamp: December 12, 2024, 03:38:59 pm
content: did you try chucking a meter across the terminals and seeing if the windings are good? I

author: elektryk
author_rank: Regular Contributor
timestamp: December 12, 2024, 03:39:30 pm
content: It is better to buy completebrush mountif you will be able to find it.

author: Ian.M
author_rank: Super Contributor
timestamp: December 12, 2024, 03:43:29 pm
content: Quote from: saaluc on December 12, 2024, 03:32:21 pmYes, those carbon blocks. Historically called 'brushes' in English as early DC electric motors used layered woven copper braid brushes for sliding contact with the commutator. Then it was discovered that the extra resistance of a carbon brush decreased arcing between commutator segments reducing wear.

author: saaluc
author_rank: Contributor
timestamp: December 12, 2024, 03:46:44 pm
content: Quote from: themadhippy on December 12, 2024, 03:38:59 pmIf you mean measuring the resistance across the terminals, yes I measured it and it was "O.L".

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: December 12, 2024, 04:15:11 pm
content: Hello saaluc ,Quote from: saaluc on December 12, 2024, 02:41:58 pmEasy peasy.You need 0.8 m of very strong cotton thread or woolen yarn. Cotton butcher twine is the best choice.Tie it to make a big loop.Roll up the large loop to have 4 small ones (because there are 4 blades).Attach each small loop to a fan blade as close as possible to the center.Hire a second person to hold the motor + fan assembly.Use a vice to hold the latter under the jaws (open those enough to that the fan rotor passes through the open jaws, but the fan case is being hold by the jaws).Pass a big screwdriver through the 4 small loops, and use it as a lever by resting on the top of the jaws.Once the fan rotor removed, you'll see 2 small Philips screws that hold the motor.Usually, it's aRC380motor with a3,172,27 to 2,3 mm shaft...A compatible one, fromRS.PS: I would not try to repair the existing motor : it will never run reliably. Just replace it with a new one.

author: saaluc
author_rank: Contributor
timestamp: December 12, 2024, 04:16:41 pm
content: As the first post indicates, the shaft of the DC motor is trapped in the fan; so the whole motor cannot be pulled out.To check the brushes (and, if needed, replacing them), is it enough to just open the holders of the cap which contains terminals and pull it out?

author: elektryk
author_rank: Regular Contributor
timestamp: December 12, 2024, 04:45:33 pm
content: Apply a bit of "dremeling" on every crimps.

author: saaluc
author_rank: Contributor
timestamp: December 12, 2024, 04:57:23 pm
content: Quote from: timeandfrequency on December 12, 2024, 04:15:11 pmFrankly, I did not understand your method.May I ask you to upload a video or at least some pictures of your method?

author: langwadt
author_rank: Super Contributor
timestamp: December 12, 2024, 05:01:24 pm
content: Quote from: elektryk on December 12, 2024, 04:45:33 pmbetter to bend them out with pliers so you can bend them back for reassembly

author: elektryk
author_rank: Regular Contributor
timestamp: December 12, 2024, 05:13:02 pm
content: Quote from: langwadt on December 12, 2024, 05:01:24 pmIt may work on this small motor, with larger ones from impact wrenches or cordless drills I prefer dremeling because it is to hard to bend them.

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: December 12, 2024, 05:34:26 pm
content: Quote from: saaluc on December 12, 2024, 04:57:23 pmYes but not this evening.

author: drhex
author_rank: Regular Contributor
timestamp: December 12, 2024, 05:40:09 pm
content: You wrap a piece of strong string around the fan blades so you can pull on them. Then you rest the fan shroud underneath a bench vise so that the shroud sits on the vise which is opened enough for the fan itself to pass through. Next you use a suitably stable lever pushed through the string to lever against the top of the vise to pull the fan of the axle. This may break the shroud, but you wouldn't have gotten it off another way then.Another idea would be to drill a hole through the center of the fan until you arrive at the axle and use a suitable bearing puller.

author: saaluc
author_rank: Contributor
timestamp: December 13, 2024, 04:37:23 am
content: Quote from: drhex on December 12, 2024, 05:40:09 pmFrankly, I was unable to understand your method without a video or some pictures. But it seems that it will break some parts. Except the DC motor, I need all the other parts for repair.

author: saaluc
author_rank: Contributor
timestamp: December 13, 2024, 04:45:56 am
content: Quote from: timeandfrequency on December 12, 2024, 05:34:26 pmExcept the DC motor, I need all the other parts for repair.Might your method break some parts?

author: CatalinaWOW
author_rank: Super Contributor
timestamp: December 13, 2024, 05:07:45 am
content: There are three methods I have seen for mounting fans like this to a motor.1. Press fit (or adhesive). The only way to remove these is to drive the shaft out using a pin punch at the hub or pull it off with something like the string approach mentioned earlier. A fixture with legs that pass through the shroud blades and catches the edge of the fan would help, and a potentially useful version wouldn't be too hard to design and 3D print. Another approach to "pulling" it off is to bend a piece of flat steel into an L shape, with the base leg of the L just long enough to slip between the base of the fan hub and the motor body. This can be used as a prying tool (preferably with one on each side working together). As stated before it is easy to damage parts with this method. Particularly if it is attached to the shaft by method 2.2. Threaded onto the shaft. Possibly with some Loctite or similar. The base method here is to grab the back of the shaft with a vise or perhaps a drill chuck and then unscrew the fan. For metal parts heat is applied to loosen any Loctite. Here there may be some appropriate solvent, but I don't have any recommendations.3. A collet. A tapered slotted cone with a hole down the center is pulled up into an external cone forcing the tapered cone to squeeze the shaft tightly. I don't see any real evidence of this type of attachment in your pictures, but there might be some clever variant, something that might work by driving the pin visible in the center down into the core. You can get a better view since you can twist and turn the part to see what might be going on.If you have a friend who is a dentist you might be able to talk him into using his X-ray machine to get a better idea of how the fan is attached.

author: amyk
author_rank: Super Contributor
timestamp: December 13, 2024, 06:00:05 am
content: It's almost certainly not threaded - there would be an obvious way of holding the shaft from rotating if it was, and motors of this size don't commonly use threaded shafts. My bet is on a press fit. The end of the fan has a convenient hole where a suitable puller's shaft can sit. You'll need a puller that grabs the hub and presses on that shaft end.

author: Simmed
author_rank: Frequent Contributor
timestamp: December 13, 2024, 06:59:35 am
content: Quote from: saaluc on December 13, 2024, 04:37:23 amlets call the nose part of of prop = the hub of the propthe string is like a little noose behind the hub1 pair tied around = all the force will rest on 2 stringso maybe it will need 10 12 14 + pairs on the hub and then another set for the plastic housing?so now you play a tug of war

author: Poroit
author_rank: Frequent Contributor
timestamp: December 13, 2024, 07:25:37 am
content: G'day saaluc,I suggest it is a press fit on a keyed or splined shaft.Do you own or have access to a drill press?1.Get some square pieces of chipboard or similar, slightly larger that the diameter of the fan body.2.Cut holes with a hole saw through the centre of these pieces of chipboard just slightly larger than the diameter of the motor.3.Stack your pieces of chipboard on the drill press table, high enough so you can drop the motor and fan into it with clearance beneath the motor.4.Use a suitable size pin punch or similar, inserted into the chuck of the drill press andgentlypush down against the shaft.5.If I am correct, you should feel them start to separate.I hope this is clear enough.

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: December 13, 2024, 09:12:21 am
content: Quote from: Poroit on December 13, 2024, 07:25:37 amSeparate : actually not, but it will probably break the whole assembly.Don't forget that the motor is attached to the plastic frame by two screws, as I mentionned earlier.Watch the motor drawingto locate the screw holes.Actually, the screws can only be safely unscrewed once the fan rotor has been removed.If you did not have such an assembly in your hands before, it is pretty difficult to figure out how to disassemble it safely. A few fails (= assembly destroyed) are required before devising a suitable method.Quote from: saaluc on December 13, 2024, 04:45:56 amNo, if you follow the method and use the tools I suggested, usually they survive.Please remember that due to their construction, these fans are made in such a way that they cannot be taken apart.

author: saaluc
author_rank: Contributor
timestamp: December 14, 2024, 03:25:56 pm
content: Thanks to all you for your insights.If I manage to unfix this fan from the shaft (for example, by the string method), can the fan be refixed strongly on the new DC motor's shaft? Or I will need a new fan too?

author: Poroit
author_rank: Frequent Contributor
timestamp: December 15, 2024, 05:40:59 am
content: Cheers timeandfrequency,Oops.....I missed those mounting screws.The tug a war method does not have any finite control on how quickly the parts separate.Both participants may end up on their backsides with a handful of broken bits........but nothing ventured nothing gained.G'day saaluc,Do you have any contacts who might have a bearing pulley you could adapt for the job?Reuse of your existing fan will depend on the new motor shaft size and type.Hopefully you can find something similar.

author: saaluc
author_rank: Contributor
timestamp: December 15, 2024, 10:29:07 am
content: Quote from: langwadt on December 12, 2024, 05:01:24 pmQuote from: elektryk on December 12, 2024, 05:13:02 pmI bent all of them out, but when I pull the metal cap, it does not come out, it does not move up even a bit. It seems that something else is preventing it from coming out. what is the solution?Update: I levered the metal cap from beneath, and it could be pulled out.One of the brushes has been broken in half and has lost contact with the collector.

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: December 15, 2024, 02:48:37 pm
content: Quote from: saaluc on December 14, 2024, 03:25:56 pmYes you can refix the existing fan rotor on the new motor's shaft. It's a press fit.If there's a brass sleeve on the existing shaft, it will need additional work, but it is still possible.Tell us a bit more about that fan assembly.Where does it come from ? What it is used for ? How much would it cost to buy a new one ?

author: Poroit
author_rank: Frequent Contributor
timestamp: December 16, 2024, 06:41:11 am
content: I bent all of them out, but when I pull the metal cap, it does not come out, it does not move up even a bit. It seems that something else is preventing it from coming out. what is the solution?Do I read this correctly?You have bent out the clips on the bottom of the motor?(attached)The fan is still attached to the motor shaft at the other end, so you wont be able to pull the guts of the motor out easily if at all.You will still need to remove the fan to access the motor mounting screws that timeandfrequency pointed out.

author: saaluc
author_rank: Contributor
timestamp: December 16, 2024, 12:57:50 pm
content: Quote from: Poroit on December 16, 2024, 06:41:11 amDo I read this correctly?You have bent out the clips on the bottom of the motor?(attached)The fan is still attached to the motor shaft at the other end, so you wont be able to pull the guts of the motor out easily if at all.You will still need to remove the fan to access the motor mounting screws that timeandfrequency pointed out.I did not want to pull out the "guts" of the motor, but I wanted to remove only the "cap". As I updated the previous post, I have now removed it. One of the brushes is broken and has no contact with the collector.

author: saaluc
author_rank: Contributor
timestamp: December 18, 2024, 04:35:56 pm
content: Quote from: timeandfrequency on December 15, 2024, 02:48:37 pmThe fan assembly is for a haidryer. There is no new one to buy.

author: Gyro
author_rank: Super Contributor
timestamp: December 18, 2024, 07:18:32 pm
content: I thought the idea, after removing the motor end cap, was to replace it, or just the brushes, to repair the existing motor without removing the fan. Otherwise there was no point in removing it.Just an example listing (I don't know the motor size but they come in standard sizes)...https://www.ebay.com/itm/285731848223Edit:

author: saaluc
author_rank: Contributor
timestamp: December 19, 2024, 11:25:17 am
content: Quote from: Gyro on December 18, 2024, 07:18:32 pmDear ChrisThank you for your insights.Best Option in terms of cheapness, is repairing the brushes of the existing cap (attached picture). Of course, repairing the broken arm is not easy.Second best option is replacing the entire cap.(Size and type of the cap:https://www.aliexpress.us/item/3256805967346108.html?gatewayAdapt=glo2usa4itemAdaptSize and type of the motor:https://www.alibaba.com/product-detail/Model-390-395-Dc-Motor-Shaft_1600088767935.html)Yourssaaluc

author: CatalinaWOW
author_rank: Super Contributor
timestamp: December 19, 2024, 11:50:45 am
content: An economical, but uncertain path to a cheap repair is to check second hand stores for a serviceable replacement, either the whole hair dryer, or salvage the motor from a similar modelOn a job I once did we had a need for a large number of hair dryers and this turned out to be a good source.

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: December 19, 2024, 07:25:57 pm
content: Quote from: saaluc on December 13, 2024, 04:45:56 amI used this method 3 or 4 times a few years ago and if you follow my instructions and those of @drhex who reformulated it in a better english than mine, and also use the tools I suggested, you won't break any part.A few cracs in the fan blades where the string was placed may appear. Remember that such a fan assembly is clearly constructed in such a way that it cannot be disassembled. So it's not really realistic to expect every piece to remain in perfect condition.It is wise to use only one unique strong string. You should put only one loop of this string around each fan blade. It is important that the pulling force is the same on each blade : you will see that the string loops will slightly slide around the screwdriver's blade (used as a lever) to provide an uniform pulling force. The more the string is slippery, the better is goes : you may use a bit of liquid soap for that.The force required is really measured in tens of kg (hundreds of N for purists).You can help by warming up the motor shaft through the existing hole in the hub of the fan rotor. Use the tip of your soldering iron, but not more than 20 seconds. If the plastic around the shaft completely melts, the fan rotor will be destoyed.I couldn't find a similar fan in my stash, so I used a more vanilla one.Here are some photos showing how to use the vice to hold the assembly, and the screwdriver as a lever.You must use a vice much larger than mine: jaws must be at least 180 mm wide, otherwise there is not enough room to place the fan assembly under the jaws.Avoid tightening the jaws against the plastic frame: the fan assembly must remain loose under the jaws.Quote from: saaluc on December 18, 2024, 04:35:56 pmWell, the price of a new hair dryer is around 20 bucks. Not sure if it's worth to mend it.

author: Gyro
author_rank: Super Contributor
timestamp: December 19, 2024, 08:10:53 pm
content: Quote from: saaluc on December 19, 2024, 11:25:17 amOuch, those brushes wore down to the point that one was 'grabbed' and dragged round to the opposite side of the commutator (you can see that it was on the verge of happening on the remaining brush), hence the sudden open circuit.If you decide to go that way, I would chose the entire cap replacement, I don't see a broken arm repair lasting.

author: saaluc
author_rank: Contributor
timestamp: December 25, 2024, 12:48:07 pm
content: Quote from: timeandfrequency on December 19, 2024, 07:25:57 pmThank you very much indeed for your detailed tutorial.