Right grade aluminium for the job

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Right grade aluminium for the job

This topic has 17 replies, 5 voices, and was last updated 27 July 2011 at 10:38 by pgrbff.

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26 July 2011 at 16:15 #72494
pgrbff
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@pgrbff
A friend has 50’s lathe and mill which I hope to learn to use. I need to machine an aluminium coupling to join a 6mm motor shaft to a spiral pinion gear for a model helicopter. The pinion has a threaded M10 x 0.5 male end, 5mm long.

I plan to use 2011 T6 5/8″ aluminium rod.

1. Is this an appropriate grade of aluminium

2. When drilling through the 5/8″ rod, do I drill an M6 hole all the way through first and then the hole to be tapped M10, or vice versa, using a centre point in between the two drilling operations?

hope this makes sense without a drawing!
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26 July 2011 at 16:15 #29442
pgrbff
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@pgrbff
26 July 2011 at 16:32 #72495
JasonB
Moderator
@jasonb
If the motor shaft is a plain 6mm shank then centerdrill followed my 6mm. Then open out a portion to 9.5mm and tap this M10x0.5 if you can get that fine a tap.

Though drilling slightly smaller and then reaming will give a better fit so less vibration at high revs

If teh motor is threaded M6 then drill 5mm and tap M6 assumeing its metric coarse which is M6x 1.0

J

Edited By JasonB on 26/07/2011 16:34:57
26 July 2011 at 16:50 #72496
pgrbff
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@pgrbff
Thank you for your quick reply. The motor shaft is plain with a machined flat which I plan to secure with a 4mm grub screw.

Does the 6mm hole do the same job as a centre drill? Or would it be better to use a centre drill size closer to the 9.5mm after the 6mm hole?

I haven’t been able to find the precise relationship between cenre drill size and hole. Should the CD be only slightly smaller than the hole you plan to drill or is it not important?
26 July 2011 at 16:50 #72497
pgrbff
Participant
@pgrbff
Thank you for your quick reply. The motor shaft is plain with a machined flat which I plan to secure with a 4mm grub screw.

Does the 6mm hole do the same job as a centre drill? Or would it be better to use a centre drill size closer to the 9.5mm after the 6mm hole?

I haven’t been able to find the precise relationship between cenre drill size and hole. Should the CD be only slightly smaller than the hole you plan to drill or is it not important?
26 July 2011 at 16:51 #72498
Anonymous
I’m sure that 2011 will do the job, but it is prone to corrosion. A counsel of perfection would be to use 7075, as this is specifically used in aircraft and has good corrosion and fatigue resistance, but is more difficult to machine.

Regards,

Andrew
26 July 2011 at 16:55 #72499
pgrbff
Participant
@pgrbff
Much more difficult to machine given the relative simplicity of what I need to do?

The piece will not be subject to anything more corrosive than fresh air and my spare bedroom.
26 July 2011 at 17:34 #72506
JasonB
Moderator
@jasonb
A centre drill is used to ensure the subsequent drills start in the centre of the work, without getting too deep into the subject a normal twist or jobber drill has a flat end so if you try to drill straight away with this it can skid about on the surface. So awith a centre drill or spotting drill which does a similar job.

For RC work I would say a BS 0 centre drill will cover 99% of what you are likely to do.

How do you propose to cut the thread? Taps of that size will be very hard to come by so you are likely to have to screw cut it in the lathe and one from the 50s may not have metric pitches

Jason

Edited By JasonB on 26/07/2011 17:37:52
26 July 2011 at 21:47 #72523
Chris Trice
Participant
@christrice43267
I made one of these for a customer just four weeks ago to do the same job. Well actually, it was for the conversion of a glow helicopter to electric. Given the torque involved, forget ali and do it in steel. It’s a small component so the weight saving is negligible and you’ll get a better grip on the motor shaft.
26 July 2011 at 21:55 #72525
pgrbff
Participant
@pgrbff
That is exactly what this is for. Do you know what model they were converting? I would be very interested. Most models these days have conversion kits available and they’re not too expensive; so it wouldn’t normally be necessary to make your own.

The commercial adapters are Aluminium, The torque involved is quite high, 3.5Kw motors spinning at 20-25k rpm.
26 July 2011 at 22:13 #72526
Chris Trice
Participant
@christrice43267
To be honest, I couldn’t tell you. It was a ‘forty’ size heli and a coreless motor but I can’t remember the details. I was presented with the body frame and told to “join that pinion to that motor shaft so that the motor sits there.” I had to fully custom turn it because the threaded section turned out to be a very non standard M10 x .75mm. That fitted the pinion gear and the whole thing was drilled and finished with a tiny boring tool to a 6mm bore to fit the motor shaft. The whole thing was done without removing it from the chuck so everything was perfectly concentric. I considered aluminium but in the interests of the client not being best pleased about having to disassemble his entire helicopter to get to a stripped adapter, I played safe, did it in steel and don’t regret it for a moment. More importantly, the client was delighted that his project that had hitherto stalled was now back in full swing.
26 July 2011 at 22:29 #72527
pgrbff
Participant
@pgrbff
If you ever find out what model I’d still be interested. My pinion is also M10 fine, 0.75 pitch, I had no idea it was that unusual.
26 July 2011 at 22:42 #72529
Anonymous
I agree that M10x0.75 is not that common, but it is not non-standard. For UK ISO metric threads M10 coarse series is 1.5mm pitch. Fine series is 1.25mm pitch and constant pitch series are 1mm and 0.75mm.

A simple Google search easily finds taps and dies for M10x0.75, and M10x0.5 for that matter.

Regards,

Andrew
26 July 2011 at 23:04 #72530
Chris Trice
Participant
@christrice43267
In the interests of cocentricity, speed and cheapness, I simply thread cut it in the lathe. As long as you’ve got the change wheels, it only takes a few minutes. Normally I’d follow up with a chaser but I’ve only got the metric standards which don’t include .75mm but careful trial and error fitting achieved a good snug fit.

Edited By Chris Trice on 26/07/2011 23:05:03
27 July 2011 at 09:02 #72550
David Clark 13
Participant
@davidclark13
Hi There

I think I bought my 10 x 0.75 from J&L Industrial.

regards David
27 July 2011 at 09:17 #72551
pgrbff
Participant
@pgrbff
They’re quite easy to buy, ebay has several.
27 July 2011 at 10:32 #72553
Chris Trice
Participant
@christrice43267
Of course that does mean buying a tap or die you’re unlikely to use again for years if ever.
27 July 2011 at 10:38 #72554
pgrbff
Participant
@pgrbff
That is why it may pay for me to get someone else to do it. I’d probably also have to buy the drill bits as well as my neighbour is American and every end mill, bit etc he has is imperial. He shipped his mill and lathe from california, and they’re industrial machines, not hobby.
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