Speed Increaser

[Roderick JenkinsParticipant @roderickjenkins93242]

[Roderick JenkinsParticipant @roderickjenkins93242]

Has anybody made Dick Stephen’s speed increaser as supplied by Hemmingway? Any comments on construction?

 

Rod

[John HaineParticipant @johnhaine32865]

I think it reverses direction so your mill needs a reversible motor.

[Roderick JenkinsParticipant @roderickjenkins93242]

John,

 

Thanks, I am aware of that. I wondered, when I put an inverter drive on the mill, what on earth use reverse would be. Now I know

 

cheers,

 

Rod

[John Stevenson 1Participant @johnstevenson1]

Rod,

 

I looked at this a while ago and wasn’t very impressed on the design.

Basically it’s a 3:1 increaser and runs in reverse as mentioned before but it only has one planet wheel running round the sun with no top bearing support, in fact it relies on the one bottom bearing.

 

The result is that the planet wheel wants to push the sun out of mesh. Dick hold the ring gear and drives the planet with the sun as driven, this gives the 3:1 increase in reverse.

 

If he had driven the ring hear, held a pair of planets and taken the drive off the sun he would have got an increase of 4:1 in the correct rotation, this using all the same parts but one extra planet gear. Plus the ability to provide a top bearing for support.

 

I can’t comment on Hemingway’s drawings which are usually good but the original MEW drawings leave a lot to be desired, for instance the sun wheel is missing and if you make all the spindle parts and come to assemble them, they are longer than the space allows.

 

John S.

[Roderick JenkinsParticipant @roderickjenkins93242]

John,

 

Thanks for those comments. I bought the kit and started manufacture without really thinking about it but have now become uncomfortable with the design. Whilst it may be fine for engraving I do not think it is robust enough for a 3mm endmill.  The drawings seem fine but could really do with a cross-section. There are some 3D views but these do not show the critical internal workings. I’m drawing up the cross-section myself and will give serious consideration to your suggested improvements.

 

many thanks,

 

Rod

Edited By Roderick Jenkins on 18/06/2011 14:49:21

[John Stevenson 1Participant @johnstevenson1]

Here is the original design as a sketch.

 

 

As you can see it relies on just the bottom bearing for support and this is just a generic ball race, not a high precision bearing.

There is no top support at all.

 

Now using the same parts, this can be achieved.

 

© 2005 John Stevenson.

 

Two bearing at the top for good support and the input, red, drives the planet wheel carries, planet wheels in green.

 

Ring gear, yellow sandwich is held and the output is by the blue sun wheel, again caried by two bearings and having an oilite top bush inside the red carrier.

 

The carrier need thickening up a tad as it’s too thin at the bottom, drawing error.

 

This design will give 4:1 increase in the same direction.

 

John S.

[PatParticipant @pat]

Hi Rod

 

I also had reservations about the torque that could be transmitted. So I started to look for a planetary gear box to act as a source of gears. I have now got the gear box guts of a Bosch industrial grade battery drill. Got these as a gift as the chucks had been wrecked and the retaining screw head chewed up.

 

The gears are designed to transmit torque. The gears and bearings show no sign of wear and the input to out put ratio is around five – difficult to hold the bits together with out the plastic case!

 

The planet gear cluster has four pinions and the over all diameter is 37mm. I will photograph the bits but may have difficulty posting so there could be a delay!

 

Phew! 

 

Reagrds – Pat

 

 

Edited By Pat on 18/06/2011 15:41:42

[Roderick JenkinsParticipant @roderickjenkins93242]

I’ve created this cross section from the Hemingway drawings, the pink bits are the gears. Clearly some tweaking will be required on manufacture to get the gears meshing properly. I’ll make it according to the drawing and see how it goes. I am a bit nervous about locating the ball bearings using only Loctite but we’ll see. It can always be dismantled and modified later.

 

Rod

Edited By Roderick Jenkins on 19/06/2011 17:15:05

[Michael HornerParticipant @michaelhorner54327]

Hi Rod

How's your build of the speed increaser coming along?

I am trying to draw up plans to build one along the lines John S suggested. HPC do a 72 tooth ring gear with a 60mm OD and Dick Stephens suggested a 16 tooth sun gear should be ok giving a ratio of 5.5:1.

The intention is to drive it with a KX3 so the top speed could be excess of 20,000 RPM. This gives me concerns about the oilite bush getting enough oil to stop it burning up! I am thinking of using 3 planets to take the strain off the sun gear. Just working out the machining sequence.

Cheers Michael

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

On a previous thread several different people suggested an alternative and simpler approach using a free running spindle driven from a small auxiliary motor .

Motor can be mounted on machine and drive by belt or in smaller power versions attached to side of spindle housing . The whole unit is just mounted on a standard tooling taper and plugged in as nescessary .

Michael Williams .

[Roderick JenkinsParticipant @roderickjenkins93242]

Michael,

It's put to one side for the moment. My thoughts are following Michael's comment above and using my Arrand spindle which is good for 8000rpm.

Keep us informed of progress.

best wishes

Rod

[Michael HornerParticipant @michaelhorner54327]

Hi Michael

I have seen the thread you mentioned but couldn't find it on a revisit. I was put off by the bulk of the design. But your mention of it has triggered the thought of use the body of the bearing housing as a pulley which will run at spindle speed, take an elastic band out to an outrigger shaft with small and large pulley then another elastic band back to to the new spindle so long as I can get a ratio 4:1 I will get my target speed of 20,000 rpm. Probably want a gaurd for the elastic bands cause i'll bet they'll sting if they snap and hit you!

Hi Rod

if the above will work I think it will be the way to go, the gears for my other design were going to cost £76 I've probably got the materials in my scrap box

Cheers Michael.

[John Stevenson 1Participant @johnstevenson1]

My design got shelved as the price of the high speed 400 Hz spindles are now really affordable and the plus side is they are so quiet.

Even at 4:1 increase you still have to run the mill flat out and get all attendant noise and vibration with it.

I'm running a 24,000 rev spindle at half speed and the noise of the cutter in the material is the greatest noise.

So far the longest it has run cutting a job was an engraving of the Mother in law which took 11 hours to cut, mind you she is a rather large lady………

[Sub MandrelParticipant @submandrel]

A bit of lateral thinking – I made a toolpost drill/mill by fitting the planetary gearbox out of a broken portable drill into a steel housing.

If you took the internals out of such a gearbox and fitted them the other way around…

Note these gearboxes are two-stage, so you could just use one stage.

Neil

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