Can I get Custom Lathe Work Done?

[mattaus]

Hi all,

I hope this is not inappropriate to post here ( I read the stickies about posting rules and it’s not mentioned…I hope) so here goes…

I need a custom piece of metal made up for me. I don’t have access to equipment let alone the knowledge and skill to make it myself. I have searched for machine shops here in Brisbane but when I remembered these forums I thought why not ask.

It’s a bit hard to describe at this point as I am not fully decided on the dimensions or material to be used yet. I figured it’d be better to find out what I can get before going about designing something way too complicated to get machined!

Long story short it’s a rotor for a brushless electric motor I am modifying. All it is, is a steel tube with an outer diameter of roughly 100mm with a 10mm wall thickness. The tube would be about 40-50mm long. It will need (at this stage) 12 flat faces machined onto the outside of the tube where the magnets will be attached. The 12 faces will likely be separated (so the edge of each flat section will not be touching the edge of another – flat, curved, flat, curved etc).

Ultimately I want to weld this tube to the attachment plate of the old rotor (that I have ground off) so some care will need to be taken to provide a welding surface. But that’s by the by at the moment.

I realise my knowledge on what is possible is limited so if someone is willing and able to do this for me I will gladly sit down with them (or via email) and nail out exactly what I want vs. what can be physically accomplished…and of course nutting out the dollars required for your time!

Alternatively if someone can recommend a better way of going about getting the piece I require made I’m all ears!

Any information would be greatly appreciated.

Regards,

- Matt

[pipeclay]

I dont mind having a go but I"m in Sydney,you may get offers closer.

[mattaus]

Hey no worries. If no one else replies I'll be in touch :2tsup:

Just to add some detail - the actual wall thickness is up for discussion. The total OD of the tube is the important part (so it fits inside the motor) but the thickness can be whatever is easiest. 10mm is only a suggestion because the magnets need a solid backing for them to perform their function correctly.

Anywho...I'll sit and wait :cool:

[pipeclay]

If no else takes it up,the rest without seeing a drawing should not be a problem,only concern may be material choice and possable distortion from welding.

[mattaus]

If no else takes it up,the rest without seeing a drawing should not be a problem,only concern may be material choice and possable distortion from welding.

n the interest of making this a bit better I'll actually sit down and draw some semi-decent pictures tonight.

Your comment on the rotor warping with the application of heat is something I never considered but it does make sense. Maybe a better idea for me to get done would be to completely replace the existing rotor with a totally new part. This would allow me to save weight, and build (in my opinion) a more robust and better suited replacement.

I'll put my thoughts into writing/visio drawings and post it back here later tonight.

[racer123]

I might be able to help out as well.
I would need some idea as well as to how accurate the spacing of the twelve flats would need to be. +- 1 degree is not to hard +- 0.01 is very difficult.
Probably best to weld the rotor together then do final outside machining and flats.
Dave

[pipeclay]

Good idea,seeing I have no real idea of what the end result will be you may be able to get away with having a thicker wall section at the welded end to help eliviate distortion,or possably a thinner section so that less heat will be generated when welding.

[Stustoys]

Hi,
I'm even further away the PC but I'm just watching out of interest.
What sort of rpm will it be doing?

Stuart

[mattaus]

I have an offer from someone in Brisbane to help me so I'll see what he can do. I will however post everything here just in case it falls through/for people who are interested.

I should stop screwing around and give all the details and let the people with a bit more knowledge than me come up with the best solution.

I am re-purposing a truck alternator as a BLDC motor. It's been done before and I'm attempting to do it better. No other reason than I'm inquisitive by nature (I'm an Aerospace Avionics Engineer by profession) and....because I can :q. It's a little project of mine basically. Beside - if it works as well as I think it will I can use it to power some insanely fast go-karts/bikes.

Part of the process is to remove the old 'claw' style rotor and replace it with, as previously mentioned, a permanent magnet rotor. This increases power, and removes the need for brushes in the motor to charge the rotors electromagnetic coil.

Here are photos of the existing rotor, still on the axle. I need to remove the rotor from the axle but I was having problems tracking down a set of clamp pliers (or whatever they are called) to remove the split ring in the open end (sort of visible in the first pic):

http://imageshack.us/photo/my-images/829/p1080311m.jpg

http://img148.imageshack.us/img148/1/p1080310si.jpg

(Argh...NFI why they won't display in the thread itself.. :~)

Anyway. The rusty rotor claw and the large inner tube (that is solid) appear to be 2 different parts, though I cannot tell how they are held together.

What I need made is exactly what is there now, but with the claws replaced with a hollow tube about 10mm thick and with the 12 flat spots. The large solid inner tube could be less thick I'm sure of it. This would reduce the weight. I'm not totally sure why it's so thick - without reading up on my alternator theory I'm assuming it's to maintain spinning momentum in order to smooth out sudden increases and losses in rpm. This is not an issue in a motor.

This will need to spin at around 4000 - 6000rpm, though that is entirely dependent on the Kv (rpm per volt) of the motor (an unknown quantity at this stage) and the ESC (electronic speed controller) I use. I'm more worried about the magnets coming off than the rotor tearing itself apart.

Could this be made from one piece of steel? The 'backing plate' the would connect the 2 tubes can be solid with a few holes drilled in it for ventilation. Or maybe it could be 3 parts, welded and then rounded up nicely on the lathe? The most delicate part would be replicating the depression for the clip ring. but even that would appear to be fairly straight forward to me. But what would I know! :sad3: Just some ideas...

As for accuracy - in this sort of application the closer the better. However +/- 1 degree is excellent, anything better is superb. I will get the flat spots to be machined a few mm wider than need be to give me room to move the magnets around before epoxying them in and wrapping the thing in carbon fiber. That's the only way they will stay put at 6000rpm.

Hope this clears some of it up. When I get the existing rotor off the axle I'll report back.

Cheers and thanks for reading.

[racer123]

Looks like you could machine the claw assembly down so the new tube goes over the top.
This can be done with no dissassembly required.
You can then weld the tube to the remains of the claw assembly.
Then machine the OD.
Dave

[mattaus]

If that's the easiest way to go about it then I'm all for it.

The only problem might be that the claw is a very tight fit at the moment (inside the stator) and once you machine that down and take into account the thickness of new tube (5-10mm) and the magnets (between 3 and 5mm) it might be too large. If you machine it down far enough to fit you might not have anything to weld the new tube to other than the existing backing plate.

Though to eb fair that was my initial idea and looking at it now it might work. Though I can't stress enough that the thicker the tube the magents attach to, the more effective the magnets will be.

If that makes sense?

[mattaus]

OK I've sat down and done the numbers on the flat surfaces required to be machined on the outside of the main tube.

The easiest solution (but not ideal) I came up with was a flat surface 19mm wide every 30 degrees.

The ideal solution (though it may be too difficult to implement) is a flat surface 6.4mm wide every 30 degrees. Either side of this is another flat surface the same width. So groups of 3 flat surface every 30 degrees.

If the second proposal can be made it would very much be appreciated.

Please see some rough sketches below. I realise the width of of the flat surfaces on the 3-group design seem almost pointless and I have considered it but I feel the magnets need as close to 100% surface contact to work properly.

http://img844.imageshack.us/img844/1594/newrotordesign.jpg (http://imageshack.us/photo/my-images/844/newrotordesign.jpg/)

I should also point out that this rotor will only be 38mm in length...so it's actually quite small.

Brain fart time:
I could also always just do the 19mm wide design, and place a thin piece (1mm thick) by 7mm wide steel in the middle of the flat spot. The middle magnet would be raised and the 2 side magnets could sit half on/half off to angle them out slightly. This would give near the same result as the more difficult to machine design without the difficult work involved.

Also in regards to racer123's idea of machining the claws down and welding the tube over the top...would it be just as much work to machine the claws completely off and then weld the tube to the 6 'stubs' that are left? This would also give the opportunity to remove some of the metal off that large inner solid tube as well (if this can be done) to reduce the weight a bit because it is ridiculously heavy.

Let me know what you all think. Do-able or completely out of touch with reality?

Cheers.

[mattaus]

Also I've tried replying to a PM stix012 sent me. After I hit send I would think the message would show up in my sent box. But it's not. So if you're not receiving them what the? But if you got 3 copies of the same email...whoops, though I have no idea what I've done if that is the case.

[Stustoys]

Those claws look cast, welding to them would be a problem if they are.
Flats 7.5 degrees apart shouldnt be a problem.
Are they round magnets? maybe a row of holes drilled with a slot drill would help hold them in place better?(although this would take alot longer.)
How are you going to balance this?

Stuart

[Stustoys]

Did you tick this box down the bottom of the page? "Save a copy of this message in your Sent Items folder."

[mattaus]

Did you tick this box down the bottom of the page? "Save a copy of this message in your Sent Items (http://www.woodworkforums.com/private.php?folderid=-1) folder."

Lol and there it is! I di'nt realise it wasn't automatic. I feel a bit silly...

Anyway the magnets are flat blocks. Due to the way motors are designed I need to use 6 to create one pole- hence the 3 rows evey 30 degrees (each section is 2 long- 3x2).

I have given no thougt to balancing yet... i guess the tube will be balanced when machined, but the additon of magnets and CF could throw that out. I migt have to use some hard epoxy on the inside of the tube to balance it out once eveything is on.

My preference at this stage is to remake the entire rotor element from a single peice of steel- so everything but the axle is gone. This would be stronger, lighter and no welding required.

Makes sense in my head at least lol. Sorry for the poor spelling mistakes...im on my phone now :s

[Bryan]

We call that 'axle' a shaft. Not welding is a Good Idea. You would have to balance the completed assembly. An engine builder who advertises balancing work could do it. But he will need somewhere he can remove material from.

[mattaus]

We call that 'axle' a shaft. Not welding is a Good Idea. You would have to balance the completed assembly. An engine builder who advertises balancing work could do it. But he will need somewhere he can remove material from.

Sorry for the incorrect terminology. Learn something new every day.

If the outer tube was thick enough he could remove some of the steel from the inner side?

Tonight after work/training I will draw up some detailed Visio diagrams of exactly what I want done. I will make it as simple as possible so less work is involved. Some finalised details:

- The rotor needs to be as close to a single piece of material as possible. If it's cheaper then 3 individual pieces can be welded together so long as the weld is very strong and the item is re-turned (is that the right word) and finished to look semi professional :;

- The material needs to be mild steel. Mild is important because of it's low carbon content. I'm not a hippy - it just has a low reluctance which is desirable when using magnets.

I'm not sure where I could find a piece of mild steel large enough for the rotor to be made from a single piece but I will start looking. If anyone knows somewhere good to go please let me know.

Once the designs are up, and anyone thinks they can do it please let me know and we can talk prices for your time. I have NO idea what to expect so I may be scared off (or rather go back to the drawing board lol) so please be patient with me. As I've stated many times this is new territory for me.

[pipeclay]

Sourcing material would best be left to the maker.
Makeing it in one piece should not be a problem.
Is the finished OD with magnets attached or just the machined rotor.

[mattaus]

The finished OD will be without magnets. Because I'm wrapping it in Carbon Fiber I have allowed 5mm for the magnets + CF (magnets are 3.2mm high).

So if the desired overall OD is 108mm, the OD of the rotor minus magnets will be 98mm (5mm each side).

I need to confirm all numbers I have written here however this will be done when I draw the detailed diagrams.

Cheers.

[pipeclay]

When you do your final calcs and or drawing you may need to do two,
one using the single magnet and the other using your 3 magnet model,as the depth of the flat for the magnet to attach too will differ resulting in a bigger finished od with magnet and C/F attached,I think.

[mattaus]

I have done some preliminary drawings. The way I did them was to draw a circle with a diameter matching the maximum allowable amount and worked backwards.

This has resulted in as you have mentioned - the depth for the totally flat magnet is larger than for the 3 flat design. This is because the greater width of the single flat cuts further into the rotor surface.

It makes sense in my head anyway. My drawings are normally accurate enough that I'm not too worried about stuffing it up ;-)