[Jonasforssell]

Hello all,

I've inherited this small milling machine from my father who was a model engineer.


The model is called Dore-Westbury Mk2 but there does not seem to be much info around on how to convert it into a CNC mill.

I'm concidering using this kit for the job.
http://m.aliexpress.com/item/713096732.html

Any thoughts appreciated from you experts out there.

Thanks
/Jonas Forssell. Sweden

[handlewanker]

Hi,.....what can I say.......first of all this mill is a bit on the flimsy side......it suffers from having a very small round column and that makes it unstable for serious milling ops.

As a Model Engineer type machine it needs a feel for the feed rate.

Best of luck if you decide to "butcher" it to do CNC type work.

The amount of money you will spend just converting the screws etc will make it economically unviable for the results you want.
Ian.

[wizard]

Hello all,

I've inherited this small milling machine from my father who was a model engineer.

Nice!

The model is called Dore-Westbury Mk2 but there does not seem to be much info around on how to convert it into a CNC mill.

There is a good possibility that this was made from a kit. It is a nice little machine for that type of use. As far as a CNC conversion I haven't heard much either. There is a yahoo group for this mill if memory serves me, so passing ideas past them may be worthwhile.

Consider the mechanics of the machine. You will need room for ball screws for the ultimate conversion or a way to reduce backlash on the conventional screws. A quick inspection of the machine should tell you if that is possible.

I'm concidering using this kit for the job.
mobile site-Germany Free Ship! 3 Axis Nema 23 Stepper Motor 23HS9430 425oz-in+Driver DM542A 50V 4.2A 128Micro CNC Router Plasma Cut

Electronics isn't the big issue. It is how you solve the mechanical issues that will be the challenge.

Any thoughts appreciated from you experts out there.

Thanks
/Jonas Forssell. Sweden

There are many considerations here, it might make more sense to sell the mill and put the money to a machine that is easier to convert.

[Jonasforssell]

Thanks for your constructive feedback!

I will use the machine for light milling only and for low precision work so I think it could make sense to go ahead anyway.

The backlash is low enough to start with. Mainly due to the fact that the machine is practically unused. I will check the space for ball screw upgrade in the future as you kindly indicated.

What are your thoughts on stepper motor capacity? Is 400 ozin enough for a machine this small?

[SCzEngrgGroup]

400 oz-in is more than adequate for such a small machine. How well those particular motors will work is another question. Those motors are quite high inductance, so their high-speed performance will not be good, and they will lose torque at higher speeds. Depending on what power supply they provide, they may never reach 400 oz-in except at very slow speeds. This *may* not be a problem on your machine, but without torque-speed curves for the motors, you won't find out until it's too late. Many people who've bought such bargain motor/driver/breakout kits have been disappointed with the performance, and some struggled to get them to even work, as they often come with no documentation. Overall, you'd be better off paying a bit more, and buying quality components, with documentation, from someone who can provide support if needed.

Regards,
Ray L.

[TiagoSantos]

I am one of those who bought similar 425oz/in motors with very high inductance. They work, but not well - like Ray said, I would need very high voltage to make up for the high inductance. Look around a bit more, it's worth spending a few more bucks to get something that will work a lot better. There are some 385oz/in and even 320oz/in motors with very low inductance that will probably have more torque at just about any RPM than the bigger +400oz motors.

As far as the mill itself - I agree that it may not be ideal for a CNC conversion.. I would personally keep it as is, or sell it to help offset a more appropriate machine. If I had something like that leftover from my dad, I probably wouldn't be able to sell it, though!

[handlewanker]

Hi, I quite agree on the sentimental aspect of the mill......it would suit someone who wants to do some small milling jobs without the need for commercial type activity, and as such you can entertain the drawbacks of the light construction seeing as J, Edgar Westbury was the designer of this machine and had the Model Engineer followers to cater for.

Most machinery used by the model engineers was of a DIY nature, and I expect this machine was probably made by the father of the poster......a real heirloom to be cherished, and I think that the machine was only available as a set of castings and not already made up.....I could be wrong.
Ian.

[Jonasforssell]

Thanks for your feedback.

The machine is as you correctly noted made from a kit of castings.
This was part of the concept and I know that my father built it himself with great attention to details.

I will not sell the mill for sentimental resons and I understand that convertimg another modern design would be a better path.

Still, my plan is to convert it with great care making sure that it can be reverted back if I would like to at a later stage.

I will check again for another set of motors with less inductance. I would be grateful for your comments on those.

Many thanks

[Jonasforssell]

Is there a post somewhere on the forum explaining the performance of stepper motors and the relation of inductance as well as other parameters?

[TiagoSantos]

I'm on my phone and can't find the link, but look at the gecko drives website, they have a really nice document about steppers and what all the specs really mean and how they affect performance

[Jonasforssell]

Excellent! Thanks.

[Jonasforssell]

Hello again Experts,

I have searched around some more and here are two candidates which I hope you will find could have a better overall performance.

http://www.aliexpress.com/store/prod...654439231.html

http://www.aliexpress.com/store/prod...587807028.html


The previous kit had 9mH inductance and 425oz-in holding torque

Any comments appreciated.

Thanks

[handlewanker]

Hi, before making any modifications do a number of test cuts with various cutters in the range you anticipate using.......the rigidity of the Dore West machine is not the best in the book but does suffice for Model Engineer type of work.

It does perform single point flycutting with some success, but end mill work is a failure at best.

I would suggest exploring the possibility of adding a bracing bracket from the head to a wall so that there will be more damping of the thrust from the cutter to the column.

The other problem is that most of the cutting depth is done with quill movement and that is short at best....moving the head casting up and down to get more clearance means you lose position........also totally impossible to use the head raising and lowering movement for Z axis work.

BTW, the nut for the smallest practical ballscrew will not fit under the table unless significent amounts of material are removed.....same for the Y axis, and that does not mean you get a double ballnut so you still get backlash eventually......the existing Acme threads do not have compensating back nuts as part of the design, but could be added.
Ian.

[Jonasforssell]

Hello experts,

I've successfully converted my mill to CNC using Mach 3 and CamBam to control it.

Calibration is completed and the backlash is quite small.

However, I ended up with a trochoid shape on my first cut.
It was made in two runs and the repetition is very good.

Only problem was that it was supposed to be a circle!
Does anyone reconize this? What could I have done wrong?

Attachment 181503

Many thanks
Jonas

[handlewanker]

Hi, probably the pitch of the screws is not what your software recognizes.

I don't think the Westbury came with a 5mm pitch screw thread.

If you have only a small amount of backlash you won't really notice it unless you are doing a lot of back and forward movement, like when you are machining a circle or making a square object with multiple cuts to get to depth.
Ian.

[LUCKY13]

It looks like you have two different pitch screws, or you slipped when entering the specs and entered two different specs.


Use a test indicator and a block/gauge of known size to measure and set your steps per. I think Hoss web site may have a good video on doing this with a gauge block (123 block or other known size gauges you may have).


Jess

[Jonasforssell]

Thank you Sirs for your help.

The issue turned out to be the Mach3 settings.
I had somehow triggered the setting for how I and J should be interpreted in the G-code.

The mill works fine now with good accuracy.
It is a great feeling to have a CNC which makes parts from your own design!

Only issue now is that the DW seems to run with some vibrations at higher rpm.
I think it might be the belt which may be uneven.

Not sure where replacement belts can be found but perhaps a standard engine belt can be adopted...

/Jonas

[handlewanker]

Hi, that was a relief.

Now that it machines to your satisfaction, it would be a good time to consider some "Improvements" that would really make it sing.

I would suggest you consider fitting Polyvee belt drive pulleys and belt, instead of the current Vee belt as it grips better and is able to flex round the smaller pulleys without suffering from belt degradation.....it also cuts out a lot of vibration.

Going a step further you might also balance all the parts of the drive train while you are about it.

The ultimate mod would be to remove the stepped pulleys and fit a 3 phase 3/4hp motor and drive the machine with a small VFD, doing away with the multi step pulley of the original design......Edgar Westbury will no doubt turn over in his grave at this sacrilegious interference with his relatively simple design, but I think he would have approved in thinking outside of the box.

There is a limit you can go due to the small diam of the column, but a head brace to a wall will stiffen that area a lot and cut out a lot of cutter chatter from the shaky head.

As it is now in CNC mode you will want to run at the higher speeds anyway, (provided the bearing layout is good), and with smaller cuts this will benefit the overall lack of rigidity.

Don't even consider modifying the head raising mechanism to give you more height as you will lose register if you do, it's something you have to live with in round column mill drills.

I think I have the original plans of the machine as drawn in the Model Engineer if you get stuck on any design details.
Ian.

[Fastest1]

Pictures?

[Jonasforssell]

Attachment 183830
Original mill.

Attachment 183832
Pulley with belt

Attachment 183834
End bracket on each stepper motor

Attachment 183836
Mount pulley onto handle

Attachment 183838
Put it all back onto the mill


And difficult things suddenly becomes much much easier to do...