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Reaming a pinion, wall thickness?

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pgrbff31/08/2011 17:17:24
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I have a motor with a 6mm shaft, and a pinion with a 5.7-5.8mm hole.
I would prefer not to remove the shaft from the motor and turn it down as this invalidates the warranty, and it's quite expensive, only 50mm long and 3.6KW!

1. How do I go about enlarging a 5.75mm hole to fit a 6mm shaft? What would be the best way?
2. This will reduce the wall thickness at one end to approximately .6mm, the overall diameter of this threaded end is 9mm, and will be screwed into a 16mm diameter aluminium adaptor which will also be fixed to the shaft with a grub screw.
 






Edited By pgrbff on 31/08/2011 17:22:59

JasonB31/08/2011 18:56:04
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I assume you get your 0.6mm wall thickness by subtracting 6.0mm from the lowest part of the helical gear, this being 7.2mm. Surely as the helical gear has been cut along the whole length of the part the wall will also be reduced to 0.6mm along the whole length not just part of it. I don't think reducing teh wall thickness by 0.1mm will make a great deal of difference to teh strength of the part.
 
My thoughts would be to hold the gear in an ER collet or failing that make a split bush to hold it so it can be reamed in the lathe.
 
J
pgrbff31/08/2011 19:22:36
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As you can see the pinion gear is stepped, at its widest, the centre section, it is over 11mm. The wall thickness will only be reduced to 0.6mm at its narrowest end, where it is threaded, and only where the grooves of the helix cut through the threads.
What sort of a reamer do I need? When I look through the catalogues there seem to be so many?
 
JasonB31/08/2011 19:28:56
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It may be stepped on the OD but the root of the gears runs along the whole length, so there will be spirals running along the whole part with a thickness of 0.6mm.
 
A 6.0mm hand reamer will do, you may want to open it out a fraction more with a drill. Before you try reaming is the gear hardened by any chance, the black colour could indicate it has been heat treated, this will likely blunt your reamer.
 
J
pgrbff31/08/2011 20:16:27
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It probably is hardened, although it is designed to turn what is probably a Delrin main gear.
The root of the gears taper off at the wider end so the wall at one end is quite a lot thicker. The motor shaft measures exactly 6mm, do I ream to 6mm or slightly wider, 6.1mm?
Are there reamers which will better handle hardened steel?
John Stevenson31/08/2011 20:21:58
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Clamp the motor, start it up and polish the 0.2 to 0.3mm off with some emery cloth.
By the sounds of the motor , 50mm long 3.6 Kw it will take it off in seconds.
 
However 3.6Kw which is 5Hp going thru a 6mm shaft sound a bit OTT to me.
Standard shaft size for 3 Kw motor is 28mm.
 
John S.
pgrbff31/08/2011 21:17:15
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The motor is approx 50mm diam and 50mm long, at 35V it spins at around 22,000 RPM. They're designed for model helicopters which weigh around 5-6Kg. with gearing of around 9:1.

Edited By pgrbff on 31/08/2011 21:18:01

Andrew Johnston31/08/2011 21:27:32
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John S:
 
I suspect the motor application is radio control models. So one, the quoted power is likely to be at some fantastical rpm. Second, a quick Google search threw up some motors of a similar size quoting 'peak power' of 3-4kW. However, there is no information about the duration over which this power is quoted. So I think it's basically 'our number is bigger than yours' marketing b******ks. It's a bit like the old audio amplifiers being rating by peak music power; essentially meaningless.
 
Apart from anything else you wouldn't half need a big battery to supply that sort of power for any sustained length of time.
 
Regards,
 
Andrew
 
Edit: Ooops, typing too slowly!

Edited By Andrew Johnston on 31/08/2011 21:28:20

pgrbff31/08/2011 22:13:25
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Thats probably why a 5A 44V Li battery can easily cost £500.00 for a 6 minute flight time and the motor and electronic speed controller another £500- £600, because they're rubbish and all R/C modellers are stupid.
My physics isn't that good, so I won't try and prove you wrong, I'm sure you'r far more clever than me.
JasonB01/09/2011 07:19:31
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Its been a long time since I had model Helicopters and with those sorts of figures I can see why people are changing from IC to electric. When I had mine inverted flight was a novelty only performed by the few, watching videos now they certainly have moved on and seem to have masses of gravity defying power. Maybe you could post a link to some flying so people can see what they perform like.
 
I did buy a little Honey Bee a while back and you do get a lot out of those little lipo batteries.
 
J
 
 
pgrbff01/09/2011 09:05:13
261 forum posts
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Not really my type of flying, even if I could do 10% of what some of these guys can do. The machine probably weighs 6Kg or so.
Edited By pgrbff on 01/09/2011 09:07:36
Edited By pgrbff on 01/09/2011 09:09:30
 
Apologies, didn't have much luck embedding link.
Is there a way of editing post in HTML?

Edited By pgrbff on 01/09/2011 09:11:49

John Stevenson01/09/2011 09:15:00
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Pgrbff,
 
I wasn't joking when i said run the motor under power and polish the shaft to fit the pinion.
Go carefully though as it's very easy to take more than 0.02mm off.
 
John S.
JasonB01/09/2011 09:21:22
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"Go carefully though as it's very easy to take more than 0.02mm off."
Just as well as he needs to take about 0.2mm off the dia
 
If you do try that method make sure you cover any cooling holes as it will suck all that abrasive dust in
 
J
pgrbff01/09/2011 09:27:26
261 forum posts
31 photos
I'm just a bit concerned that no matter how careful I am I won't get a very precise fit to the pinion. The shaft has quite a long flat (for grub screws) along almost all of its length.
The other reason I hoped to leave it 6mm is that there is the possibility of supporting the far end of the shaft in a bearing, 6mm ID.
I'll get there in the end but I have only recently received all the various parts required and they each came from a different continent.
Terryd01/09/2011 12:51:54
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Posted by pgrbff on 31/08/2011 22:13:25:
...................
 
My physics isn't that good, so I won't try and prove you wrong, I'm sure you'r far more clever than me.
 
 
Hi pgrbff,
 
Andrew is quite clever as us who have been here a long time know. I'm not so clever either though, but let's try.
 
Unless it's changed since i was at school 50 years ago (you never know with Europe),
 
Watts = Volts x Amps, so in your case:
 
3.6kW = 3600W = 35V X Amps
 
Amps = 3600/35 = 103A (approx)
 
There again, I'm probably wrong being so thick, but someone will correct me, and after all, Amps ain't Watt they used to be
 
Regards
 
Terry
 

Edited By Terryd on 01/09/2011 12:52:40

pgrbff01/09/2011 13:36:12
261 forum posts
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I know from my data logger that I can draw up to 80A during flight, and that is gentle sport flying, I would get roughly twice the flight time of the chap on YouTube. 80A x 50V is 4Kw. Obviously this isn't constant, but the motors do get very hot and I wouldn't be pushing it at all. The motors in my models are barely warm. My speed controller is rated at 80 A constant, most flying the same model and similar setup would use 120A ESC.
I lied, I can do the sums, just a little annoyed at flippant remarks when I'm looking for help with things I don't know verymuch about. Thanks for the support.
Windy01/09/2011 14:50:27
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Regarding these high power electric motors etc.
The speed record club news letter reports that an electric motor- cycle at the Mojave Mile track in the California desert achieved 190.6mph and that was not on full throttle because of wind buffeting.
The bike is powered by 108 Lithium-ion cells in three packs and has a booster pack of six Lithium-ion polymer cells to give maximum power availability.
The electric tethered model hydroplanes are also going fast as well.
 
Windy
John Stevenson01/09/2011 15:46:06
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Posted by pgrbff on 01/09/2011 13:36:12:

I lied, I can do the sums, just a little annoyed at flippant remarks when I'm looking for help with things I don't know verymuch about. Thanks for the support.
 
 
My remark about the Kw / HP question wasn't flippant.
I was interested in how a motor of this power can transmit that power thru a 6mm shaft.
 
75% of my full time work is repairing commercial electric motors, many with the shaft ripped off and they are all greater than 6mm.
 
John S.
chris stephens01/09/2011 18:42:26
1049 forum posts
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Hi Guys,
Boy oh boy, I had heard that flying a model helicopter was difficult and after watching that You-Tube I can see what they were talking about. That pilot sure did well, after starting quite nicely, he then completely lost it for three minutes or so, but luckily he got it under control before managing to land it safely.
chriStephens
Ian Parkin01/09/2011 19:35:54
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Why doesnt the pinion fit the shaft to start with?
Is it a scratch built heli you are making?
if not what do the manufacturers of the pinion want that to fit...5.75 seems a funny size to arrive at when the motor shafts are 6mm or are some motors 5.75?
 
Ian
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