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HankMcSpank
18-06-2013, 09:45 PM
Nema17 motors driving 1204 ballscrews? ...that ok? ...or will I see the CNC police knock on my door?

Ok, here's my dilemna.

My first machine I built (a rite of passage I think)...been there done that...my engineering skills suck & therefore my machine sucked - I won't be building anymore.

My Second (present) machine a modest sabel 2015 (http://www.cnc-sable.nl/images/sable%20text.jpg) ...fairly well constructed, certainly rigid enough for the stuff I cut (pcbs & the odd bit of acrylic)...the problem is insufficient accuracy. This machine uses bog standard M10 threaded rod & drive nuts of uknown parentage/pedigree (but I suspect are in the delrin accuracy scheme of things) ....& I'm now milling quite small SMD PCBs - I need more accuracy (& ideally a bit more speed...I do like a whizzy machine)

So, I could just upgrade my present machine to a new one ...but I've a penchant for fixed gantry machines (I like how much quieter they are - I've neighbours & a wife to consider as I do this in a spare room) & they're not that common....in fact they seem quite rare - especially those fitted with ballscrews/nuts.

I've found a Chinese supplier (http://redsail.en.alibaba.com/product/937226128-212518060/2013_new_style_mini_cnc_router_made_in_China_RS_30 20.html) ....bottom line is it's gonna cost me the guts of a grand after import duties etc & to be honest I don't even need the extra size (it a 3020...not that big...but still bigger than my 2015)...just the accuracy. Now to me, a grand seems a lot to pay for the small gain in accuracy I seek over my present machine!

That said it seems well made & specced, for example, here's the innards of the control box ...

http://hostmypicture.com/images/controlbox.jpg)

(at least it's not a woeful Yoocnc stepper driver single pcb board in there!)

So then I wondered could I just simply upgrade the leadscrews on my existing machine to ballscrews/ballnuts (total cost would be approx 100 - I like!) ...having done the measurements & looked at ballnut dimensions, I think I might just be able to get away fitting SFU1204-3 ballnuts onto my present machine ....but my Sabel 2015 machine has small nema17 motors with 5mm shafts...would this be a crazy match for 1204 rods? (alas, IMHO it's not going to be practical to upgrade the motors to nema23...on account the present nema17 casing edges are flush with the rear of the CNC gantry uprights...if I replaced with nema23....two of the NEMA23 mounting holes would see fresh air at the back (ie they'd had nothing to screw into)...at a push I guess some form of plate could be made to allow me to use nema23, but then the project gets bigger (& like I say, I suck with anything involving metal/accuracy!)

therefore I think I might be stuck with nema 17s...so like I say, would nem17s be be too much of a mismatch for 1204-3 ballscrews/nuts, the spec of the motors on my machine is here...

1. Step angle: 1.8 degree
2. Number of Phase: 2
3. Hold torque: 4.4 kg.cm
4. Rated current/Phase: 1.68 amps.
5. Phase resistance: 1.65 ohms
6. Voltage/Phase: 2.77 VDC

Thanks in advance.

ptjw7uk
19-06-2013, 09:50 AM
If the machine moves now with standard screws then it will be easier to move with any ballscrew.
Will there be enough room for the ball nut!
Have you thought of smaller ballscrews 10 mm!

Peter

Swarfing
19-06-2013, 11:36 PM
Hank 1204 will be fine but you will need to mod the Z plate to take the Ballnut by the looks of it?

HankMcSpank
20-06-2013, 10:05 AM
Thanks guys


Hank 1204 will be fine but you will need to mod the Z plate to take the Ballnut by the looks of it?

I haven't taken the Z backplate off to have a look, but I think the X axis ought to take a 1204 ballnut (which according to the spec sheet - http://images.tiu.ru/22699355_w640_h640_sfu1605.png ...top entry, not the highlighted entry in that table!), should fit...

http://hostmypicture.com/images/wp000199.jpg

Can anyone tell me the difference between a 1204-3 & a 1204-4? (& no smart replies saying 1 please!)

I think I'm gonna stay with this machine a little while longer, cos yesterday I found & ordered a dedicated spindle which looks like it suits my needs (& until yesterday I didn't even know existed)....

http://hostmypicture.com/images/spindle.jpg


a video of it in action (spindle porn!)...


http://youtu.be/OAnzf7MM8MA

the spiindle, motor & mounting plates (everything in the picture) only totals 66 plus 15 delivery - which to me seems very keenly price (nice & quiet too...and 10,000RPM ought to be enough - my present spindle only goes up to 5,000rpm)...so I pulled the trigger & should have it in about 10 days.

Swarfing
21-06-2013, 06:50 PM
Great news sounds like it is all working out in the end. Will you stand the stepper off so that you can get a support bearing in there?

HankMcSpank
21-06-2013, 09:07 PM
I think the Z axis is gonna be a challenge (it doesn't appear to be the same as the X axis & not sure I can fit an sfu1204 ballnut in there at all :-( )

Swarfing
22-06-2013, 12:15 AM
Is there space between the linear bearings? could always make a new block up so as not to ruin the existing.

GEOFFREY
22-06-2013, 01:14 AM
That spindle assembly looks really good and excellent value. I can't comment about the noise as I can't hear it!!!(only the cleaner). G.

HankMcSpank
22-06-2013, 01:24 AM
That spindle assembly looks really good and excellent value. I can't comment about the noise as I can't hear it!!!(only the cleaner). G.

Ironically, having just bought asbo's 300W spindle (which is a surprisingly fine spindle type for the price) ....the one I've now just gone and bought afterwards (above) looks to have exactly the same driving motor on it - they are just gearing up the motor's RPM with the pulley (I note they quote the motor at 24V vs. "upto 48V" that the 300W spindle motor is normally spec'ed for - I guess the spindle that the motor is driving only has modest bearings & wouldn't cope well with RPM above 10,000RPM - actually, perversely, I'm hoping the spindle *doesn't* use ceramic bearings & therefore the spindle shaft might be groundable - is that a word?)

Re the noise...as someone who mainly mills PCBs, I'm a sucker for a quiet spindle, and yes it's very quiet, which is why I pulled the trigger so quickly (the seller had sold 4 & only had one left)...only last week, I was comtemplating water cooled spindles, but I'm pleased I didn't now...I really don't need the extra grunt (& complexity/weight) that it yields.


Is there space between the linear bearings? could always make a new block up so as not to ruin the existing.

It's all too easy to reason that most members on here are of a solid engineering background ilk...I'm not - really small children laugh loudly at my output (I often hear them muttering things like "FFS, that bloke should have used angular contact bearings on his Z axis"...I have no idea what they're going on about).

I'm a reluctaant CNC'er ...I potter along blindly, then hit a problem ...& spend way too long trying to find an inadequate solution! (whereas, I'd much rather be playing my guitar & gulping on a cool one)

Swarfing
22-06-2013, 01:55 AM
LOL! Hank no inference from me on that score, firm believer in you can only do what you can only do :-)

GEOFFREY
22-06-2013, 11:49 AM
LOL! Hank no inference from me on that score, firm believer in you can only do what you can only do :-)

My belief is that you can do anything if you really want to and are prepared to put time and effort into it. I will be 70 in august and would like to think that I learn something new every day. Probably left it to late to become a brain surgeon now, but I don't really want too!!! G.

HankMcSpank
22-06-2013, 12:11 PM
My belief is that you can do anything if you really want to and are prepared to put time and effort into it. I will be 70 in august and would like to think that I learn something new every day. Probably left it to late to become a brain surgeon now, but I don't really want too!!! G.

I agree with the sentiment (I probably undersold myself under the influence of a caipirinha last night), but alas I'm not that literate when working with metal/engineering (I haven't got the chops to fall back on....electrons yes....metal no!)....but I agree when faced with a challenge, most folks can solve it *if* they are driven & really need a solution! (oh yeah....& *if* they hang on places like this where people are so gracious with their time & knowledge :afro: <---this afro icon bears no relevance, I just figured it'll likely never get an outing here, so used it!)

Lee Roberts
22-06-2013, 04:39 PM
I posted the link to your new spindle on ebay in the wrong thread Hank. :worked_till_5am:

I think the price is great for what you get and was thinking if you did need more than the 10k RPM, now you have the option of changing the DC motor and this maybe easier to do: ER11 Spindle for Sable-2015 / SPD-ER11 (http://www.mycncuk.com/forums/routers-spindles-controllers/6215-chinese-300w-dc-spindle-spindle-shaft-grounded-post46486.html#post46486)

.Me

Jonathan
23-06-2013, 05:16 PM
The efficiency of a ballscrew is typically over 90%, compared to maybe 30-40% for a threaded rod which relies on sliding friction, so you would expect a big increase in feedrate. The torque required to accelerate the ballscrew would be greater due to the increased diameter, however since the pitch is greater the required angular acceleration is actually less, so overall you'll be much better off with the ballscrew.
The main reason for ballscrews having higher efficiency is they rely on rolling friction, not static friction, so you may want to consider trying the method I demonstrated here (http://www.mycncuk.com/forums/router-build-logs/4901-buildingafloat-4.html#post33577), where the screw nut is replaced with a bearing at an angle resting on the threads. That converts the drive to mostly rolling friction, so the efficiency is greater, plus it's also easy to get very low backlash. It's a very cheap way of upgrading, but I'd still stick with ballscrews if you can fit them in due to the accuracy (among other things).

Perhaps by using timing belts and pulleys to drive the screws you could fit in bigger motors? You could also use a favorable ratio to get higher resolution for milling PCBs. Incidentally, what feedrate and spindle speed do you currently use?

66+15 for that spindle seems a lot to me when compared to the cost of the small brushless motors and controllers from hobbyking. Granted they're not that quiet, but I'm sure you'd find ways round that. The substantially higher RPM should make up for that too, since you could cut the PCBs faster.

HankMcSpank
23-06-2013, 07:00 PM
Thanks for your input Jonathan.


Perhaps by using timing belts and pulleys to drive the screws you could fit in bigger motors? You could also use a favorable ratio to get higher resolution for milling PCBs. Incidentally, what feedrate and spindle speed do you currently use?

Well my previous spindle only spun at 5,000rpm (which was my limiting factor wrt pcb milling feedrate), so I kept the feedrate at about 200mm per minute (which is painfully slow).

The 300w chinese spindle turns at about 8,000rpm @ 32V - the spec suggests it can spin as high as 12,000rpm at 48V...but I wouldn't want to run it that high, cos I'm pretty sure it'll be stressed & its life will be dramitcally reduced. But even so, I've won a bit of feedrate (up to 320mm per minute I guess). My main win moving to asbo's chinese 300w spindle is noise (it's unbelievably quiet) & also weight ...because including bracket, the spindle chinese 300w weighs just over 1kg (vs 2kg for the Proxxon bfw/40e plus bracket)...therefore I can push my rapids faster too.

The spindle I've now also just bought off ebay (pictured further above) spins at 10,000rpm @24V, so I guess I can up the feedrate to 400mm per minute with it (btw, I have no idea what a normal feedrate is for pcb milling?!)


66+15 for that spindle seems a lot to me when compared to the cost of the small brushless motors and controllers from hobbyking. Granted they're not that quiet, but I'm sure you'd find ways round that.

I must be one of the few folks on here whose main priority is noise (I'm not blessed with a shed in the garden, garage, workshop etc)...so noise is of major concern.....and I've precious little time enough to be working to address any noise issues introduced by a noisier, more powerful (or faster) spindle.

Re the cost of the spindle...well a basic 300w motor & mounting bracket (which drives the spindle) costs about 47 alone (delivered) on Ali-Express , so an extra 34 I paid, gets the milling spindle, backplates, pulleys & belts including delivery from Asia.... personally, I think that's great value.

GEOFFREY
23-06-2013, 09:21 PM
Well, I still think that spindle assembly is good value for money. I know that I could never make it to sell at that price. G.

Lee Roberts
23-06-2013, 11:14 PM
Well, I still think that spindle assembly is good value for money. I know that I could never make it to sell at that price. G.

I agree, I dont think you could build a spindle using a brushless motor for less, let alone whats in that package.

.Me

Swarfing
24-06-2013, 10:39 AM
The 'time' and 'effort' to make the parts alone would cost more.