Reaming a pinion, wall thickness?

[Ian PParticipant @ianp]

Going back the original posters query about opening up the bore of the pinion…..

 

At the high RPM that this motor is going to be operating at its important that the pinion is a good fit and accurately centred. If the pinion is hardened then tho only real option is probably use an internal toolpost grinder (I’ve never used or seen one that small but they must exist).

 

Depending on the manufacturing quality of the existing pinion its possible that whilst the ID and OD of the pinion might be perfectly concentric, the chord diameter of the gear teeth may not be. To go to great lengths making this gear fit may not be worth it.

 

I think I would be looking to find a pair of gears with the right bore diameter. Since this project already requires some engineering work I would also reposition the pinion on the motor shaft so that it is as close as possible to the motor bearings. The clamping device (a grubscrew is not ideal at these rpm) can then be outboard of the pinion.

 

I have had some experience of brushless ‘Outrunner’ motors and what amazes me is, even the quality ones are not that well balanced, and, as was mentioned previously even the bearings dont seem up to the job.

 

Ian P

[Clive HartlandParticipant @clivehartland94829]

firstly the supplied gear may have been supplied as such so that it can be reamed to fit!

It would also seem that normal grub screws will not be adequate to transmit the torque that is avaliable.

It may need flats machined onto the shaft and dog point grubs screws fitted.

A query, I am assuming these electric motors are ‘Ring Field’ type.

As regards the motor shaft I would do nothing to it and only work on the gear.

An internal grinder, toolpost type will give no better finish than a reamer for that application.

 

Clive

 

[JasonBModerator @jasonb]

Looking at other posts about this conversion it would seem that the adaptors are retained by grubscrew though as clive says a flat on teh shaft would help a lot. You can also see why just trying to find another pair of gears is not going to be easy as the tail rotor gear is part of it and probably also has an autorotation clutch for engine off landings.

 

Just one question, how are you measuring the bore of the pinion, at a small size like this a pair of digital callipers will tend to under read so it may be closer than you think.

Do you have any old 6mmId bearings you could measure in the same way and see what size you get?

 

 

 

J

 

Edited By JasonB on 02/09/2011 07:43:12

[Ian PParticipant @ianp]

Initially when I saw these last two pictures the reason for not wanting to start again with another pair of gears became more understandable. I then realised that they are not pictures of the actual posters helicopter.

 

The upper bracket seems to be just a bearing housing as it does not look large enough to mount a motor, whether electric or IC.

 

It was not clear from the original enquiry but I now assume that the motor is fitted with the shaft pointing upwards with the pinion supported at both ends. In which case this topic has gone round in circles somewhat but it does boil down to finding some way of opening the pinion bore!

 

Out of interest, what are the drilled flange on the aluminium pulley boss for? maybe the clutch?

 

Ian P

[blowlampParticipant @blowlamp]

The question has been answered. If it’s soft enough, put the gear in a collet and drill/ream it. You can test with a file or scriber on some unimportant area to see how hard it is and if either of these tools skids over the gear, then it will probably have to be ground.

 

Do you think one of the Loctite products would help to hold the gear in place?

 

 

Martin.

[Clive HartlandParticipant @clivehartland94829]

If the supplier/maker is anything like HPC then the gears can be supplied hardened or soft.

HPC list all sorts of gearing.

 

Clive

[pgrbffParticipant @pgrbff]

Although the pictures, one of which I have not seen before, well done with your search, are not my machine, it is the same model. A JR Sylphide 50.

 

1 There is a flat ground along almost the entire length of the shaft – this is one reason why I did not think the emery cloth idea would work very well, as has been stated, the shaft needs a good fit.

2 It is entirely normal to fasten the pinion to the shaft with a single loctited grub screw,

3 The little wings are used to hold magnets that a governor sensor would pick up, I do not need these. This part is not designed for this mod, but was useful as it worked. Unfortunately it is no longer available.

4 The only way I have to measure is standard calipers, and I get inconsistent readings, so to be honest I am not entirely sure what the ID is. I will have to go to a friends house who has a full set of numbered drill bits and see how close I get.

5. Finding a pair of gears is out of the question. There is a tail drive gear attached to the main gear and this all sits in a hub containing a one way bearing to allow autorotations.

6. The upper support bracket, gold anodised, has two bearings. The bottom larger bearing has a 9mm ID and the wider end of the pinion is loctited into it.

7 The upper bearing would have previously centred the IC engine starter shaft, ID 5mm. I had intended changing this for a 6mm ID bearing which would centre and support the motor shaft at its upper extremity.

 

It is not strictly necessary for the shaft to pass through the pinion. This seemed a good idea as it would ensure the motor etc were precisely aligned and would allow the motor shaft to be supported at its upper end to increase the life of the motor bearings.

 

I think I need to try and ream out the pinion, I’m sure it can’t be too hard, after all it runs against a plastic gear.

 

1 Will a 6.1 reamer be a suitable size for a precise fit of the 6mm shaft.? It wll be difficult to assemble the various parts in the model if it is too tight.

2 Assuming I use a 6mm reamer, what size should the hole be before I ream? How much material is a reamer designed to remove? Very little I imagine.

 

 

 

 

 

 

 

Edited By pgrbff on 02/09/2011 10:03:32

[Clive HartlandParticipant @clivehartland94829]

It is assumed you have access to a lathe? if that is the case then as said before put it in a collet and open the hole to 5.8, this is erring on the side of safety, incase a 5.9 overcuts.

The idea is to leave 5-10thou for the reamer to cut.

Use a 6mm reamer and using a thin oil and a slow speed ease the reamer into the hole and withdraw frequently. Keep flushing with the oil and slowly advance through the hole, again withdrawing and flushing.

WD40 can be used and will help flush away any debri that the reamer cuts.

Once through the gear with the reamer, offer up the motor shaft and it should be a soft push fit.

De-burr both ends with a countersink by hand!

The speed should be the slowest possible.

The only way you will get the hole bigger than 6mm is if you use an adjustable reamer which will be very expensive for you.

The whole process is a very simple job and is carried out by model engineers all the time.

 

Clive

[pgrbffParticipant @pgrbff]

Thank you.

When I was browsing reamers there was a large difference in cost. Will spending more make the job easier or will the more expensive reamer simply stay sharp longer?

Will a hand reamer do in a lathe, or do I need some other type?

 

Should the steel prove to hard, what symptoms will I observe, so that I know to stop.

 

[blowlampParticipant @blowlamp]

Posted by pgrbff on 02/09/2011 10:24:40:

Thank you.

When I was browsing reamers there was a large difference in cost. Will spending more make the job easier or will the more expensive reamer simply stay sharp longer?

Will a hand reamer do in a lathe, or do I need some other type?

 

Should the steel prove to hard, what symptoms will I observe, so that I know to stop.

 

 

Arceurotrade have the 6mm reamer you need for less than a fiver.

 

As I said in my previous post, just test the hardness by seeing if you can scratch the pinion bore with a file or scriber etc. If the tool skids along the surface without starting to bite, then it’s going to be too hard to cut with a reamer. No need to press hard when doing the test, as a sharp tool will cut without undue effort.

 

Martin.

[pgrbffParticipant @pgrbff]

A small round needle file appears to bite. If the hole is smaller than 5.9mm, say 5.7mm, what is the best way to open it out before reaming?

Paul

[Ian S CParticipant @iansc]

Do as Martin says, test with a file before you start, anb if the file cuts the metal you are ok to ream the bore. Then just follow Clives instructions—- all done.

I was reading about these small motors, and was interested to see that some of the ones designed for boats are water cooled to allow longer running at high power. Its amazing the amount of power they squeeze out of such a small package! Ian S C

Edited By Ian S C on 02/09/2011 11:32:28

[pgrbffParticipant @pgrbff]

It’s just I am truly a beginner. I wasn’t sure if you could simply drill out a 5.7mm hole to 5.8mm with a standard drill? It seems so little material to remove.

[blowlampParticipant @blowlamp]

Tell us what equipment you have access to, such as lathe, collets, chuck and drills etc.

You can drill in stages of 0.1mm if your tools are OK – you could even bore that pinion in the lathe, but it depends on your skill and equipment.

 

Martin.

Edited By blowlamp on 02/09/2011 11:48:15

[pgrbffParticipant @pgrbff]

Bridgeport Mill and can’t remember brand of lathe but probably as big and as old as mill. Both belong to a friend who only uses them occasionally. I buy all the tooling myself.

[blowlampParticipant @blowlamp]

Let us know how you get on.

 

Martin.

[pgrbffParticipant @pgrbff]

Will do but have to order reamer and bits from UK, so will be a while before I get started.

Thanks for all your help.

[JasonBModerator @jasonb]

You should open it upto 5.8 as said, the risk of reaming it from anything smaller can make the reamer cut oversize.

 

Just about any hand reamer you buy will be whats called an H7 tollerance which will fit your shaft just fine. The advantqage of a hand reamer is that it has a tapered end so will easily follow the existing hole. Definately do not get a 6.1mm reamer.

 

One point not mentioned is you should not reverese the lateh or turn the reamer backwards when withdrawing it, again that may make it cut oversize.

 

Oh and you have seen that picture, I snipped it from the video you posted about the motor mounting bracket.

 

J

[pgrbffParticipant @pgrbff]

I have ordered a Hertel reamer and 5.8mm Hertel jobber bit.

One thing I had not considered in any detail that has come back to bite me is how am I going to hold the pinion in the lathe?

I currently only have 2 options, a quality 3 jaw (vice?), and imperial 5C collets.

The OD of the pinion is 11.5mm.

Any answers that are economical appreciated.

 Would a 12mm 5C collet work? I don’t want to damage the gear.

edit again, I have found an inexpensive 11.5mm 5C collet, I assume that would be OK or is there a better route? 

Edited By pgrbff on 02/09/2011 17:34:01

Edited By pgrbff on 02/09/2011 17:38:26

[JasonBModerator @jasonb]

5C should only be used for their exact size.

 

Back at the beginning of this thread as an option to using a collet I suggested a “split bush” and thats likely to be your best bet as due to the teeth on the pinion a chuck may not grip truely.

 

A spilt bush is easy to make, get a bit of alloy bar a few mm larger dia than the pinion say 16-18mm dia and face of fa length about 20mm long. Hold it lightly in the lathe 3 jaw and drill then bore out to a snug fit on the pinion, mark one chuck jaw and the bush were it touches the jaw. Remove bush from lathe, split the bush with a hacksaw opposite the mark and de burr.

 

Put teh pinion in the bush and grip the bush with the marks aligned, you will then have a good true hold of the pinion with no risk of damaging the teeth.

 

Its easier to do than explain, if you want a pic of a bush let me know.

 

J

[pgrbffParticipant @pgrbff]

No I get the idea.

You may not have seen the edit, I can get a 5C 11.5mm collet. I understand the collet fits into a Hardinge ? holder?. Would that be as good as the split bush?

I can see an aluminium split bush would be soft and grip well.

 

[JasonBModerator @jasonb]

If the collet is not expensive then go for it. If you have a bit of aluminium laying about making the bush would be good practice for when you come to make the adaptor and probably cheaper than the 5C which you may never use again

 

Edit

 

Has your friend got an 11/16″ collet thats probably withing the tightening range of 11.5mm, may save a few quid.

 

J

Edited By JasonB on 02/09/2011 18:21:12

[pgrbffParticipant @pgrbff]

He has all the 16ths, but not many 32nds. Is 7/16 or 11.11mm close enough? The 11.5mm is £7 inc post, I may just bite the bullet.

I hope I won’t have to do too much more shopping for this, its getting expensive!

[Clive HartlandParticipant @clivehartland94829]

Expensive! Join the club. I have built up tools over 40 years and I still need other types of cutters and collets. Its never ending and when I look at my Sockets and spanners that I have had to buy over the years for different cars its amazing.

Drills should be a one time buy in a set and you can buy extra sizes as time goes on.

Taps and dies are another expense which sometimes are cheaper by the set!

Enjoy what you are doing and do not worry too much about it as most times it will all work out well.

 

Clive

[JasonBModerator @jasonb]

Actually the 7/16″ may be pushing it a bit so go for the 11.5mm

 

J

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