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12 hours ago, -missy- said:

 

Hi Bill.

 

I did consider trying one of those gearboxes out but one of my requirements was to try and reduce the noise the machine makes when running. I thought that the noisy brushed motor plus a metal gearbox would make the noise even worse. Its a big reason why I decided to go for a nice quiet brushless motor and belt drive.

 

I don't have any doubt the gearbox will help and fit the machine well. Usovo seem to make good quality stuff. The machine does run far too fast so slowing it down does help lots.

 

Julia.

Thank you Julia. I am not too confident of doing things as drastic as changing the motor as yet.

 

Bill

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this thread has turned into triggers broom stories  :jester:

 

all power to your elbows  my proxxon stands unfettled although I did get the very expensive  vice  brilliant for drilling holes I  consider converting to cnc  but unless my 3d design  work improves would be a waste

 

Nick B 

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10 hours ago, richbrummitt said:

Did you do anything special where the lead screw attaches to the table?

 

Hi Rich.

 

The original uses plain bushes (blue) and some steel profiled plates (red) on the ends,

 

image.png.97dc2899674d789c223ff35da223db01.png

 

I replaced these with some profiled Brass plates with a way of mounting some thrust bearings (2 on each axis).

 

image.png.86a9ec0aa98e9806b9b87906808570d1.png

 

As for the area where the leadscrew nuts live, I basically chopped out the mounts for the nuts and replaced them with some brackets made from Aluminium allowing for some adjustment to make sure there was plenty of opportunities to make sure things aligned well.

 

image.png.672954f1ad9f7138b2a729004e310365.png

 

It seems to work well.

 

Julia.

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19 hours ago, Nimbus said:

I'd be very interested in seeing details of the brushless motor conversion. The noise from the standard setup is pretty obtrusive!

 

The Nim.

 

Hi.

 

Its not what I would class as an easy mod. You have to make a few bits...

 

The original setup uses a splined socket which the motor locates into (red). As I was replacing the motor, I had to make a shaft to suit. Fortunately at the end of the original shaft, there is a M6 thread so I made the replacement shaft screw into that.

 

image.png.02b7dae605aef79605cf56e6310d04d7.png

 

image.png.2125800b52b72ad8b3543e35940a2aab.png

 

I also designed and made a plate (3DP) that sits onto of the original housing, this was designed to mount the new motor along with a top bearing for the new longer splindle shaft.

 

image.png.2f3376cb63af7c3d06e7592b2e32e4b6.png

 

Choosing a brushless motor is a bit of a minefield as there are so many variations. In the end I went for this one as it meant I could use a 12v 20A power supply.

 

https://www.componentshop.co.uk/lc2835-9t-900kv-outrunner-brushless-motor-leopard-hobby.html

 

The motor is mounted inside the original Proxxon housing and it drives the spindle through a 3:1 belt reduction along with the ESC controller for the motor and a repackaged servo tester which is used as a speed controller.

 

image.png.77fb4cd3ff68fdd1749f3658f45f1f65.png

 

image.png.75f477a9d583f2521c952f45415b3624.png

 

As I mentioned, it is not an easy mod but it is so worth it. The new brushless motor is significantly quieter and along with the speed control and belt drive reduction, I can now run the machine at more sensible speeds.

 

Julia.

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1 hour ago, Enterprisingwestern said:

Can I send you mine?, that's all way beyond my engineering skills.

Mike.

 

Hi Mike.

 

You can but it will cost you lots of money! :P

 

Julia.

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5 hours ago, -missy- said:

I also designed and made a plate (3DP) that sits onto of the original housing, this was designed to mount the new motor along with a top bearing for the new longer splindle shaft.

 

There could be a market for that!

 

The Nim.

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I looked at the Proxxon but for the reasons given above decided against it and bought a Clarke CMD10 Micro Milling / Drilling Machine instead. More expensive but didn’t need any modifications and was suitable straight out of the box, particularly the RPM. 

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On 07/10/2020 at 15:14, -missy- said:

 

That's weird, I got asked the same question too. My spindle runout is around 0.02mm, I would be very happy to use it if it was 0.002", you will be hard pushed to get a machine spindle of this type to run any better really, that is more than adequate for our stuff.

 

Not weird at all. Same person doing the asking :)

 

My standard spindle has about 2.5 thou runout measured on a cutter shank in the (Proxxon) collet. There are other reports online of circa 3 thou runout on the Proxxon spindle. The problem with this is several-fold. Firstly you get a cut that is oversize (3 thou is a fair percentage for a 1mm cutter). This error does manifest itself if using CNC to cut out shapes (and can be compensated by fudging the cutter diameter when generating g code). Secondly there is a high probability that you will only be cutting on one flute instead of the whole cutter. It also stresses the cutter more which is not a good thing with carbide. They do break and if you have significant runout then that will make them break sooner.

 

There was a long discussion started by a chap on the Model Engineer mag forum a few months back. He ended up bolting a whole new Chinese motorised spindle to his MF70 which is a bit extreme (and not cheap) but it worked for him.

 

Having measured sub 1 thou runout inside the collet holder taper, I tried a tip from another contributor to the same thread - to make a new collet with a much tighter fit in the parallel part of the holder. This needs some accurate lathe work and it took me two attempts to make one satisfactory 3mm collet. My runout came down from 2.5 thou to a tad under 1.5 thou. I was hoping to get under 1 thou but it's still an improvement... plus of course making a new collet only improves matters for the collet size that you make.

P1070570.JPG.971cf41f611e4f4449d12d73f977e850.JPG

 

Another comment on the same thread was to the effect that the Proxxon cutters appear optimised for cutting non ferrous metals and also stick out a long way from the Proxxon collets (which doesn't help with either runout or stress). I've now bought a 1mm stub length cutter from Arc Euro trade which should stick out less far and has a more pronounced flute spiral. I can't comment on its performance yet because I have not needed to do any 1mm cutting since buying it.

 

Regards, Andy

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  • RMweb Gold

 

Not being fully versed in the niceties of engineering, but if the various inaccuracies are inbuilt into the machine, does it not mean that it is the wrong machine for people who are looking for high accuracy at minimum tolerances, and they should be looking at a basically better machine.

The Proxxon does the job I want of it, although the expert may throw their hands up in the air, it can cut/file/mill/drill more accurately than I can do it by hand.

 

Mike.

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1 hour ago, D869 said:


 

My standard spindle has about 2.5 thou runout measured on a cutter shank in the (Proxxon) collet. There are other reports online of circa 3 thou runout on the Proxxon spindle. The problem with this is several-fold. Firstly you get a cut that is oversize (3 thou is a fair percentage for a 1mm cutter). This error does manifest itself if using CNC to cut out shapes (and can be compensated by fudging the cutter diameter when generating g code). Secondly there is a high probability that you will only be cutting on one flute instead of the whole cutter. It also stresses the cutter more which is not a good thing with carbide. They do break and if you have significant runout then that will make them break sooner.

I did a lot of research on imaging dental burs cutting at high speed using high resolution optical microscopy. It is always the case that there will only be one blade cutting in a TC bur at any time. The others will act ‘in support’ but essentially they are always unbalanced. Run out of bearings or chucks is obviously a no-no, but the errors in individual burs can be quite large. High quality modern manufacturing techniques will doubtless have improved on this, but there is little doubt that you get what you pay for. 
 

Tim

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4 hours ago, Enterprisingwestern said:

 

Not being fully versed in the niceties of engineering, but if the various inaccuracies are inbuilt into the machine, does it not mean that it is the wrong machine for people who are looking for high accuracy at minimum tolerances, and they should be looking at a basically better machine.

The Proxxon does the job I want of it, although the expert may throw their hands up in the air, it can cut/file/mill/drill more accurately than I can do it by hand.

 

Mike.

Likewise - mine does the job I need. There is a pretty big jump in price and size when you look at alternatives so I have no plans to change it. Incremental improvements, however, are well worth a look.

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Proxxon have a new heavier-duty Universal milling system head unit ref  UF/E due out soon. It takes ER11 collets so has better tool dia capacity than the MF70. Brushless DC motor, 10-30k RPM. Dual 20mm Micromot and 43mm standard European spindle collar.

 

https://www.proxxon.com/en/micromot/20200.php

 

UK stock due  Jan / Feb 2021, price around £300.00 incl VAT.

Edited by EHS
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1 hour ago, Enterprisingwestern said:

 

is there a simpler, less engineeringly complicated way to put a decent motor in the MF70, or at least some way to control the speed of the thing?

Mike.

 

Hi Mike.

 

The only options I can think of are to either replace the speed control for something a bit more flexible for driving the motor or fitting some sort of gearbox like the USOVO planetary gearbox.

 

Julia.

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5 hours ago, Enterprisingwestern said:

 

Whilst the method previously mentioned is obviously successful, is there a simpler, less engineeringly complicated way to put a decent motor in the MF70, or at least some way to control the speed of the thing?

 

Mike.

Here is a link how to reduce the speed of the MF70 adapting the original controller board:

https://www.instructables.com/Reducing-the-Speed-of-the-PROXXON-MF-70/

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Julia,

 

The brackets you made for te hob and the MF70 look like 3D prints.

Are these accurate enough direct from te printer of do you have to machine them afterwards?

And do you need a very sophisticated printer for parts like this?

The hob looks very professional :)

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Thank you Jan.

 

The parts were printed on a FDM machine. It makes producing parts for these mods so easy!

 

https://www.prusa3d.com/original-prusa-mini/

 

I haven't had to do anything other than ream out (by hand) a couple of holes on some of the parts. So far it looks like it is going together really well (there is still quite a bit to do) but I will use a DTI once complete to check the critical dimensions.

 

Julia.

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9 hours ago, -missy- said:

Mini Hob is progressing...

 

image.png.81065f85749047ad30f3ed30911a3096.png

 

J.

 

Sorry if this just shows how thick I am but can I ask please, what is a mini hob? It looks very interesting and nicely made whatever.

 

Izzy

 

 

 

 

 

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What type of motor is in the Proxxon?

I’m sure there was a thread on here about replacing the motor in a Unimat 3 with a sewing machine motor. It strikes me if the motors were similar you could use the sewing machine foot control to vary the spindle speed?

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Ah, thanks Julia.  I am a dunce when it comes to cnc stuff, but do I take it that is will be used in conjunction with a cnc mill? Mounted on the coordinate table. That programming the stepper motor(s) will allow it to rotate relative to the hob cutter?
 

My hob cutting setup was/is purely ‘old skool’ and totally mechanical, the arbour containing the gear blank being driven from the cutters drive via gears and shafting.

 

If you can arrange it so it can be set at any angle relative to the hob cutter then gears of any helix angle can be cut with just the one hob. And of course with any number of teeth. Beats using involute cutters hands down. And of course machine taps make good cheap hob cutters if you are prepared to accept the different pressure angles and smaller tooth depth. But I would guess you know all this stuff. 


Look forward to seeing it completed.

 

Izzy

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