King Midas mill conversion

Subject of conversion in this thread is a mill from 1980's.

Attachment 5426

There are some underlying issues that I would hope to address during the conversion:
- huge slack on Z-axis (covered here in detail: http://www.mycncuk.com/forums/showth...g-a-conversion )
- large slack on both X and Y -axis

Have read as much as possible, trying to learn from other machinists build-logs. As a result, here is a draft shopping list
- items in blue relate to axis/ballscrews.

ITEM NO.	PART NAME	Length	QTY
1	Nema 23 stepper motor, 3Nm (425 Oz-in)	-	3
2	PM752 Microstepping Driver		3
3	Power supply 400W	-	1
4	Coupling	-	3
5	MBA motor mount	-	3
6	X, Y, Z-Axis Ballscrew Fixed Support Block, FK-type		3
7	X-Axis 1605 / C7 ballscrew 581mm + ballnut	581mm (520mm usable thread)	1
8	Y-Axis 1605 / C7 ballscrew 346mm + ballnut	346 mm (285mm usable thread)	1
9	Z-Axis 1605 / C7 ballscrew 386mm + ballnut	386mm (325mm usable thread)	1
10	Ball nut housing (X,Y,Z-axis)		3
11	X and Y-Axis Ballscrew Floating Support Block, FF-type		2
12	Z-Axis Ballscrew Floating Support Block, BF-type		1

In view of the mill, please can anyone spot here
1) Something clearly wrong ? (something one would regret later?)
- eg. size of motors

2) USB vs. parallel port
- that is something I keep on thinking. Have read about arguments for / against.
- Kind of would like to go USB, but I have read parallel port is the right thing to do.

3) Cables and sundries
- worried about little bits missing from the list. (trying to buy all in one go, to save on shipping fees)


For now I have left out from shopping list "pulleys" and "belts". Hope could have this machine running some day, then later add belts/pulleys. Not sure how this conversion is going to turn out, will it run or not.

Motors and drivers are a good choice. What voltage is that 400W PSU?

I would substitute the couplings (4) for timing belts and pulleys. It makes it much easier to mount the motors as no faffing about getting them on concentric, reduces resonance and allows you to choose the ratio to get either better resolution or speed.

For (5),(6),(11),(12) make your own as you can use the milling machine to make them better than the commercial ones and much much cheaper.

USB / Parallel. If you use USB I doubt you'll regret it, but why not try the parallel port first as it costs virtually nothing to try?

For the stepper motor cables most people use 4-Core CY, 1.5mm^2 cable. Also add E-stop switch, limit switches and connectors for stepper motors.

Quote:

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Originally Posted by Jonathan

Motors and drivers are a good choice. What voltage is that 400W PSU?

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- The one I was looking at, is this. Is it any good?

Wattage 400 Watts
Input Voltage 240V AC
Output Voltage 36V DC adjustable +- 2.5V approximately
Output Current 11 Amps

Quote:

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Originally Posted by Jonathan

I would substitute the couplings (4) for timing belts and pulleys. It makes it much easier to mount the motors as no faffing about getting them on concentric, reduces resonance and allows you to choose the ratio to get either better resolution or speed.

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Think I just started to like belts and pulleys.

Not sure if one wants more speed, at 5mm pitch. Thought of going lower pitch, even 2mm, but most of screws available seem to be 5mm.
- Perhaps my preference is machine / cutter longevity and accuracy.

Quote:

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Originally Posted by Jonathan

For (5),(6),(11),(12) make your own as you can use the milling machine to make them better than the commercial ones and much much cheaper.

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In my calculations,perhaps half budget is for mounting hardware. On Ebay there seems to be great bargains, for example I like these mounts:
http://www.ebay.co.uk/itm/Aluminium-...item3f148563db

Good an idea to make home-made mounts etc., though worry a bit about increased complexity.

Quote:

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Originally Posted by Jonathan

why not try the parallel port first as it costs virtually nothing to try?

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Good point, parallel it will be.

Quote:

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Originally Posted by Jonathan

For the stepper motor cables most people use 4-Core CY, 1.5mm^2 cable. Also add E-stop switch, limit switches and connectors for stepper motors

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Going now back to drawing board, I will soon come up with a more detailed shopping list. Thanks Jonathan for comments, they are very helpful.

The proposed set up looks good for a backlash of around .015 -> .025mm if you get it right. Plenty good enough to remake the machine after the screws bed in and .025 mm start to hack you off, which it probably will :smile:

A stepper does 400 half steps per rev. A 5:4 belt reduction on to a 5mm screw would give you 0.01 mm per half step, add one microstep for .005 mm and it becomes credible. You could reduce it 5:2 and avoid the springy microstep but that could seriously affect your rapid at 36 volts.

Quote:

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Originally Posted by diy-john

- The one I was looking at, is this. Is it any good?

Wattage 400 Watts
Input Voltage 240V AC
Output Voltage 36V DC adjustable +- 2.5V approximately
Output Current 11 Amps

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No good, why spend more on 70V drivers then use them on only 36V? The torque from a stepper motor is inversely proportional to speed and proportional to voltage, so if you get a 70V PSU you will get almost twice as much torque from the same motors. It's risking to operate right on the limit, so look for something just under 70V. One of the cheaper ways to do it is to use a toroidal transformer.

Quote:

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Originally Posted by diy-john

- Perhaps my preference is machine / cutter longevity and accuracy.

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Cutter longevity is a vague one... if you feed a cutter too slow it can break just as quickly as from cutting too fast. You need to estimate the feedrates required for the materials you wish to cut taking into account the range of cutter diameters. Then make sure it will go a bit faster to be sure. However clearly you don't want to optimise the system for a high feedrate, and thus low resolution, if the vast majority of the time you'll be using much lower feedrates. You could select different size pulleys for each axis and swap them round / experiment to find the best compromise.

Quote:

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Originally Posted by diy-john

In my calculations,perhaps half budget is for mounting hardware. On Ebay there seems to be great bargains, for example I like these mounts:
http://www.ebay.co.uk/itm/Aluminium-...item3f148563db

Good an idea to make home-made mounts etc., though worry a bit about increased complexity.

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It should be decreased complexity if you make your own mounts for pulleys. This is what I started out with on my milling machine as it was easy to make without CNC and does the job. You can see them, briefly, in some of my very old videos:

http://www.youtube.com/watch?v=tasl9...eature=channel

Quote:

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Originally Posted by Robin Hewitt

The proposed set up looks good for a backlash of around .015 -> .025mm if you get it right. Plenty good enough to remake the machine after the screws bed in and .025 mm start to hack you off, which it probably will :smile:
...
You could reduce it 5:2

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Robin, with this rate, the mill will be cutting a couple of atoms per slice - maybe. :smile:

So far, added to shopping list some 48 teeth (around 75mm diameter) pulleys, and smaller 24 teeth (around 35mm diameter). Could make it into 5:2, guess it will be a bit more precise then.

Quote:

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Originally Posted by Jonathan

No good, why spend more on 70V drivers then use them on only 36V?

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Good Jonathan you say that, didn't even come to think about that. Updated into shopping list. So far only found some 50V PSU's, but will keep on looking, to add to the list.

	Shopping list colour codes:
	RED=NOT NEEDED, going DIY
	ORANGE=Maybe not needed (DIY?)
	GRAY=check quantity
	PALE BLUE=Ballscrews+ballnuts as units
	YELLOW=New since last list
ITEM NO.	PART NAME	QTY
1	Nema 23 stepper motor, 3Nm (425 Oz-in)	3
2	PM752 Microstepping Driver	3
3	Power supply 50V – 68V, at least 400W	1
4	Coupling	3
5	MBA motor mount	3
5	Aluminium motor mount	3
6	X, Y, Z-Axis Ballscrew Fixed Support Block, FK-type	3
7	X-Axis 1605 / C7 ballscrew 581mm + ballnut	1
8	Y-Axis 1605 / C7 ballscrew 346mm + ballnut	1
9	Z-Axis 1605 / C7 ballscrew 386mm + ballnut	1
10	Ball nut housing (X,Y,Z-axis)	3
11	X and Y-Axis Ballscrew Floating Support Block, FF-type	2
12	Z-Axis Ballscrew Floating Support Block, BF-type	1
13	Pulley for 12mm width belts. AT5 -type. 24 teeth. Total width circa 22mm. Total diameter circa 37mm. For X, Y, Z -axis	3
14	Pulley for 12mm width belts. AT5 -type. 48 teeth. Total diameter circa 75mm, for X ,Y Z -axis	3
15	Belt 12 mm 12AT5 length circa 450mm, for X, Y-axis	2
16	Belt 12 mm 12AT5 length circa 330mm, for Z-axis	1
17	E-stop switch	1
18	Limit switches	6
19	Connectors for stepper motors	3
20	4-Core CY, 1.5mm^2 cable

Quote:

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Originally Posted by Jonathan

http://www.youtube.com/watch?v=tasl9...eature=channel

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Nice video Jonathan. Makes it easier to understand how the pulleys are setup.
- 6, 11, 12 ... not quite sure how involved a procedure it is to make them DIY? (and how big a saving can be made, and can one create those without CNC? )

Think the shopping list starts to look quite good (ready to go?). Really appreciate, your help has been great. Thank you!

Here is a new draft of the ballscrews. Lengths change a bit, from going to pulleys/belts instead of directly driving the screws
.Attachment 5442

A ball screw is best held in tension by Belleville washers to compensate for thermal expansion, one thrust race at either end.

If you lengthen the XY shafts at one end you can keep the handles.

Run the table to it's ful travel and ask yourself where the CNC parts are going to fit in the available space.

Experience tells me that being new to this you are very unlikely to believe this is necessary. You feel a compelling desire to see it cutting, don't want to go back to the drawing board now and spend extra money on machining screws. I only mention it so I can say, "Told you so" later on :naughty:

Yes Robin, back to drawing board it is. Really appreciate your advice, glad I didn't yet buy wrong length ballscrews. :smile:

Went to garage, moved X/Y -axis back and forth full travel. Need to lengthen the ballscrews, pulleys would now crash to the table.

Not only that, but realized that it might be possible to extend X/Y -axis travel a good couple of inches, with minor changes.
- Had not really thought, where one would fit the ballnut, and where screw would be mounted. (attach ballnut to upper part (the one sliding), or lower part vs. the other way around, that kind of things)
- Below is a sketch of the Y-axis movement (current vs. possibly future). Changes would be: 1) a longer ballscrew; 2) attach ballscrew to the table that does not move; 3) attach ballnut to the table that moves, at the centre.

Attachment 5443

Quote:

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Originally Posted by Robin Hewitt

Belleville washers to compensate for thermal expansion, one thrust race at either end.

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This is all new to me. Thanks will look for pics from google. Another thing I don't quite understand yet, is the construction of the "fixed mount" for the ballscrew. (still thinking whether to buy ready made, or DIY).

Quote:

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Originally Posted by diy-john

Yes Robin, back to drawing board it is.

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Wow! If you are okay to take advice you can make one hell of a machine. I got it right on my third set of screws when the penny finally dropped.

Problem is, you need a CNC mill to make a pretty CNC mill which is why I was suggesting you cobble something together first. Hope you have a lathe, really do need a lathe.

I used pairs of Belleville washers to apply a preload of 500 lbf. One pair for each screw to hold the axial bearings in tension, one pair for each double ball nut.

That means there is no play in the system, apart from the column bending, so long as the load does not exceed 500 lbf. It was a lot of work but is quite delightful to use and all self adjusting.

The XY screws appeared much too long until it was all together, have a pic...

Quote:

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Originally Posted by Robin Hewitt

The XY screws appeared much too long until it was all together, have a pic...

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Robin, that is one sweet looking machine. One can tell, a lot of planning has gone into it. Like the kind of contrast with the big, sturdy, used Warco mill, and then the precise CNC -parts. Very cool.

King Midas conversion last couple of days has been measuring + and thinking how/where conversion related components will be. From all your comments, I have realized how distant my thoughts have been from this project. Feel one has been watching this project sort of from cloud -level, but now there is need for much closer look. Exciting.

1) Y-axis ballscrew -related
1.1) Ballnut would be attached to "lower", "stationary" bed of the mill. (view from front of the mill)

Attachment 5448

1.2) Y-axis ballnut would be attached to "lower", "stationary" bed of the mill. (side -view, from right hand -side of the mill)
- white box, height is 55mm, width is 18mm (for reference only)
Attachment 5449

1.3) Overview / sketch of Y-axis ballscrew (side view, from LEFT -hand side of the mill)
- colours have no specific meaning, just different colours for different components
- length of ballscrew is now at 508mm. (note how it has grown, initially one was going to buy a 346mm screw...LOL)

Attachment 5450

1.4) A challenge in Y-axis ballscrew is a 35mm vertical space here
- thought initially there is 40mm space, since the "cave" bottom looked like level with "outside" (see picture attached)
- need to make DIY "slim" ballscrew floating end-mount. Haven't found a slim-enough ready made mount.
- SKF 7200 BEP bearing outer diameter, for a 16mm diameter screw, is 30mm
- Would mount screw to "moving upper deck".

Attachment 5451


I haven't got a lathe yet. Tool/workshop -wise I am in the wrong league. Looking to do premier league, but my skills/tools are only 5th division. But thanks to this forum and careful planning, maybe this game is possible..

You will need to get the ends of the 16mm screws turned down to 12mm and partially threaded 1mm pitch.

Watch out, 12mm single row, angular contact bearings don't have dust shields, you will want to bury them in grease.

You can't use double row bearings with shields because they aren't crushable.

This is how I built up my Y screw assembly...

I put on one bearing
the aluminium mount that bolts to the machine
then another bearing
then a pair of Belleville washers
then the pulley
then a stepped iron sleeve to carry the indicator dial and the handle
then a 12mm half nut

I nipped in flat ended grub screws through the iron sleeve and pulley, flats cut on the screw shaft.

I wound the 12mm nut in one turn to preload the Bellevilles and crush the bearings.

Then I added another 12mm half nut to lock the first one.

Then I tightened the grub screws.

There was no need for a bearing at the far end of the Y screw, it simply isn't long enough to whip.

Robin, tried to understand how things would go on the ball screw. Now, this is getting to the far edge of my knowledge, this is all new.

Made a sketch of how I have understood:


Attachment 5459

So, starting from the right hand side, in the picture, requirements for machining screw:

- Machine 12mm length of screw to 10mm diameter (if want a bearing at the far end of the screw). Moving further from right to left, add

Quote:

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Originally Posted by Robin Hewitt

I put on one bearing <--- 1 bearing, shaft=12mm, OD=32mm, W=15.9mm, like this http://3.bp.blogspot.com/_3D8MX6Q_YG...G_0326+sml.jpg so machine ballscrew width=15.9mm diameter=12mm
the aluminium mount that bolts to the machine <--- For this, machine 3mm length of ballscrew diameter=12mm. Bearings will go mostly inside this mount(?)
then another bearing <--- machine ballscrew width=15.9mm diameter=12mm
then a pair of Belleville washers <--- like this http://www.trakar.com/spring-trainin...rings/disc.jpg machine 2mm length of ball screw to diameter = 12mm
then the pulley <--- machine total width of pulley (eg. 25mm) diameter = 12mm + flat spot
then a stepped iron sleeve to carry the indicator dial and the handle <--- machine total width of pulley (eg. 25mm) diameter = 12mm + flat spot
then a 12mm half nut <--- machine a thread M12 x 1mm to the end of the screw, perhaps for a length of 10mm

---

OR: machine the screw like this:
http://www.slidesandballscrews.com/images/machining ball screw-1100mm.jpg
- Except no.1 : that there would be a longer piece of screw machined to 12mm diameter (perhaps 35.8 mm length instead of 23mm in picture, to allow 2 x bearings (30.8 mm) + bearing housing (3mm) + belleville washers (2mm) = 35.8mm
- Except no.2 : Make a 12mm "flat spot of 50mm length" (to take pulley and handwheel)


For now, this project focus is trying to understand requirements: how / to what specification machine ballscrews.

Please comment!

Thanks!

Can you read an AutoCAD .dwg or .dxf? My drawing is a bit chaotic but it's al there if you look hard enough. I draw to get the dimensions then draw individual pieces for cutting.

I have lots of 12mm Belleville washers left, the minimum order was generous. I can send you half a dozen for the three screws if you PM an address, may take a while to find them though. I may have some 16mm I used for the ballnuts, spec is at www.bellevillesprings.com

Robin, your offer is very generous, thank you very much. Will send you a PM.

Did not realize how critical these ballscrews are to the build, and how much thinking has to go to them.

The X-axis, which I have so far thought as being "the piece of cake" in this project, and hence did not really think about it much.

Today thought better still check available space for X-axis ball screw.

- X -axis ball screw would have to go through this hole:

Attachment 5469

- The hole height is equal to 28.66mm, which sounds great when you think it is only a 16mm ballscrew to put in there.
Attachment 5470 Attachment 5471

- However it comes so close, because the ball nut height = 40mm, and the nut must clear the moving "top deck" (which slides over the ball-nut).
Attachment 5473

Think there will be only 0.66mm of air underneath the screw, if one will go for 16mm screw. (and if the screw really is 16.00 mm). Challenge is, that one can not move the ballscrew higher, because then the ball nut would not clear the sliding "top deck".

A bit frustrating perhaps to just measure and measure, when one wants metal chips and sparks to fly. But guess you really don't want buy ballscrews that are only good to post to classifieds section... so slowly it goes. :)

Quote:

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Originally Posted by diy-john

Did not realize how critical these ballscrews are to the build, and how much thinking has to go to them

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If you get the ballscrews right you never notice them. Get them wrong and you will be for ever adjusting and compensating.

I can export that drawing as a PDF if you think it might help, I have never exported anything as a PDF so I don't know.

Robin,
Try http://sourceforge.net/projects/pdfcreator/ which will give you a "printer" that will allow you to print from cad or any application and give a pdf file.

In most conversions of machines of this size that i have been involved with the ballnut between the X and Y needed to be the FSI of DFI type that has two fixing holes either side of the flange and 2mm lower profile than the standard FSU type.
This will get over you space problem.

Quote:

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Originally Posted by Gary

FSI of DFI type that has two fixing holes either side of the flange and 2mm lower profile than the standard FSU type.

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Thanks Gary - Please do you know the "height" of the lower-profile ballnut, for a 16mm diameter screw (1605)?
- Have used 40mm in my calculations, thinking might have by coincidence already used a lower profile version(?)
- If one could get 2mm lower than 40mm, then it would be great yes.

With a bit of help from Robin, latest draft -version for X -screw is here:
Attachment 5475

Total length of screw now is 871mm. (it has grown an extra 290mm from the original plan).

Hope that "custom" screw would not break the bank. (don't know how much extra cost that machining will add on top).
- Have prepared to go "conventional" cuttings, too, if it becomes really dear.
- One facet: want to get the screws as good as possible
- Another facet: being a newbie at this, would be very, very surprised if one gets it right first time round. Not sure how much point there is in paying top money for ballscrews, only to want something else next month. Of course trying very hard to get it right first time, but have to be realistic.

Slowly forward..

Lots of drawings on Gary's site:

http://www.zappautomation.co.uk/ball...2cf54c2f87cf0d

I can machine the ballscrew as you've drawn it for £15 plus postage.

Quote:

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Originally Posted by diy-john

latest draft -version for X -screw is here

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The X screw is best held in tension, suggest you put a thread and one bearing at either end.

I have found 31pcs of the 12mm Belleville washers I used...
www.bellevillesprings.com pn: D2812215

You are welcome to half a dozen, just shout.

Was going to mention adding the second thread for tensioning but for some reason I thought that drawing was for the Y-screw...oops. I've got a thread on both ends of my router X-axis screws for the same reason.

Do you reckon the D2812215 Belleville washers would be suitable for preloading RM1204 ballnuts? The screw I have here is actually 11.60mm diameter so it's going to close... Apparently 10-15% of static thrust rating is a good compromise for preload, so 1KN. I probably need a lower spring constant for that as such a small deflection will be hard to measure.

Quote:

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Originally Posted by Jonathan

Do you reckon the D2812215 Belleville washers would be suitable for preloading RM1204 ballnuts?

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I used them with 1204's on my Roland mill at considerably lower pre-load than on the Warco. I don't go above 5mm tooling on that.

Works okay, but agree a lighter section washer would be easier to adjust and give you more take up.

Looking at the drawing is seems over complicated.
If you want zero backlash and don't want any movement on the support bearing just go for a good quality FK12, the gten R1605 ballscrew and the R1605T3-FDID-P1

This is the link to the datasheet for the FDI and FDU type ballnuts and it is 34mm between the flats, so it is actually 6mm difference.
http://www.zappautomation.co.uk%2Fpd...%2FFDU-FDI.pdf

The ballnut is already pre loaded for zero backlash and has been tested on the screw.

you will need ti install chinese fonts in acrobat.

Quote:

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Originally Posted by Gary

The ballnut is already pre loaded for zero backlash and has been tested on the screw.

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That looks interesting, is it shimmed or does it have springs? The data sheet is vague.

No its a spacer between the two nuts.
I dont know of any commercial double ballnuts that use a spring.
All the manufactures i have worked with use a spacer to pre load the double ballnut, and there are reasons for this.

Quote:

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Originally Posted by Robin Hewitt

That looks interesting, is it shimmed or does it have springs? The data sheet is vague.

---

Quote:

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Originally Posted by Gary

All the manufactures i have worked with use a spacer to pre load the double ballnut, and there are reasons for this.

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Good point, I forgot to mention that John will need to leave room to fit an oil pipe to the nut. I use 4mm OD nylon tube and standard push fittings which are a bit sticky out and it will drip :beer:

Quote:

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Originally Posted by Jonathan

I can machine the ballscrew as you've drawn it for £15 plus postage.

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Wow, cool Jonathan. Can't go wrong with that. Thanks!

Quote:

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Originally Posted by Robin Hewitt

www.bellevillesprings.com pn: D2812215

You are welcome to half a dozen, just shout.

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Robin, yes please, need those.

Quote:

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Originally Posted by Robin Hewitt

suggest you put a thread and one bearing at either end.

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Made another draft of X-axis screw. Please is this any good now?
- added a thread to the other end. And also a similar "structure, a fixed mount" for the ballscrew. So there are now two such mounts, one at either end of the screw.
- there are two (2) screws in picture below, but it is the same one single screw.
-- The other one just highlights, what components would fit, and where. Like hand-wheel, pulley, shims, Belleville washers.

Attachment 5483

Not sure about the dynamics, kind of figured out, that with this setup, the Belleville -washers + half nuts at either end of the screw ---> would tension the screw sort of around either end fixed mounts. Please correct if you think one has mis-understood the principle.

Quote:

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Originally Posted by Gary

This is the link to the datasheet for the FDI and FDU type ballnuts and it is 34mm between the flats, so it is actually 6mm difference.
http://www.zappautomation.co.uk%2Fpdf%2FBallscrews%2FFDU-FDI.pdf

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Gary, the 34mm height ballnut gets me off the hook. Thanks for pointing out these alternatives. Will speak to you about other components.


Thanks!

Robin - thank's for confirming that about the washers. I'll order some 'lighter' ones (http://www.leespring.com/uk_product_...ype=W&subType=)

Quote:

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Originally Posted by diy-john

Wow, cool Jonathan. Can't go wrong with that. Thanks!

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:) Discuss details when the design's ready.

To put the screw in tension you don't want to have pairs of angular contact bearings at both ends, as that fixes both. You need a pair of angular contact bearings at one end, and a standard deep groove bearing plus Belleville washers and thrust bearing at the other end to provide contact force for the tension. If both ends were fixed rigidly with angular contact bearings the tension in the screw would depend on the relative spacing of the bearing blocks and the length of the screw between them, so there's no way to set it.

By 'standard washer' I assume you mean an accurately machined washer with parallel faces. You don't need a washer between the ballscrew end and angular contact bearing as the bearing is most accurate resting on the machined shoulder on the screw.

That looks horrible. I'm obviously not explaining this at all well.

To put the screw in tension you just need one angular contact bearing at either end. The Bellevilles try to stretch the entire screw end to end. Adding more bearings just gives you an alignment nightmare. There is hardly any side loading on the screw to worry about, so don't worry. I used one bearing at either end of my overlength X screw and it was fine and dandy.

I used a pair of bearings at the handle end of my Y screw simply because I couldn't fit any bearings at all on the far end.

Not a problem for the X so I put one bearing at either end.

The whole she-bang should be sloppy, right up to the moment you tighten down on the Belleville's.

You are all doing a good job explaining the principles.
- It was me who assumed X and Y -axis ballscrews are put together in similar way.
- Assumed too, that idea is to make it as sturdy/rigid as possible.
- There are some gaps in my knowledge, filling the gaps with assumptions doesn't always work

But it will be good. Will create another drawing of the ballscrews -setup.

Thanks again for comments!

... and only one pair of Belleville washers, you don't want to balance the screw between two springs because that can move.

A few design tips.

I bolted the X screw pulley solid to the inner race. I sprung the sleeve that takes the handle at the other end. This reduced the bearing overhang I couldn't avoid on the Y.

Putting the handle on a sleeve means I can pop the handle off without detensioning the screw. Handy if I want to work on something that overhangs the end of the bed.

I mounted the X motor facing the unlikely way round and extended the screw to get clearance on it. This makes it a lot easier to mount, easier to change the belt and easy to pop a cover over to keep the crut and fingers out.

My X motor mount isn't actually bolted to the machine, it's free to turn. I was going to Loctite it in place but found the 500 lbf screw tension quite sufficient to hold it. I lean on it occasionally, if it ever moves I will know I have lost tension.

Quote:

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Originally Posted by Robin Hewitt

To put the screw in tension you just need one angular contact bearing at either end. The Bellevilles try to stretch the entire screw end to end.
I used one bearing at either end of my overlength X screw and it was fine and dandy.

---

Thanks again Robin

Please would this setup make the X-ballscrew dandy? (is this what you mean?)

Attachment 5500


Sorry if this obvious to some of you. I tried to figure it out, that
- if you now tighten the screws at each end of the X-axis screw ---> the nut(s) will push the Belleville washer ---> the Belleville washer will push the bearing ---> the bearing will push the fixed bearing mount. But because the bearing mount is fixed, then tightening the nut(s) will pull (try to stretch) the screw from either end.

Please correct. (is this getting better or worse? Tell me)

Thanks!

Try this pic for the X screw in tension... :smile:

Right hand nut down tight.

Left hand nut tensions the screw.

Personally I'd put the pulley at the other end to reduce the overhang.

I should have drawn the handle fitting bigger than the nut. That way you can put the handle on and off without removing the nut.

Edit: I should also have put the Belleville washers on the other side of the pulley so the pulley grub screw doesn't have to slide. I can redraw it if you want.

Cool Robin :) - Thanks!

That picture is worth a thousand words. Updated X-axis draft accordingly.
- added Belleville -washers on the other side of the pulley, like you say
- the sleeve, on top of which the handwheel comes is a nice feature.

Attachment 5503

Quote:

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Originally Posted by Robin Hewitt

Personally I'd put the pulley at the other end to reduce the overhang.

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Now, have thought about this overhang. Might as well say now, what I have had in mind, but before reading further, make sure you sit tight and don't spill any coffee.. :lol:

The challenge is, that the X-axis movement is a mere 220mm, though the table is 500mm wide.

Thought of moving the
- handwheel
- pulley
- motor

way out of the end of the table, on the right hand side.

Attachment 5504

Attachment 5505


This "extension" would change X-axis movement from 220mm to around 400mm. Think there might be challenges ahead, with accuracy/slack, at the far end of the X-table movements. However, I have reasoned, that perhaps one could bring the slack down with careful adjustment. Just have been thinking, that there may be situations, I would rather live with a small slack at far end, than reposition the object on the table (because of lack of X-axis movement).

Of course people will wonder, why one didn't buy a larger mill in the first place. But what do you think, is this "extension" something one definitely should not do? Please comment :)
- extension would not be for attaching, or supporting pieces on table, but rather bring out the X-axis motor, pulley, bearing block.

On my mill the original handle / bearing arrangement already clears the casting that the bed runs on. The extra travel that 'gains' has proven invaluable on numerous occasions. As you say it's bound to not be as rigid as using the standard travel, but I've never noticed it.

You could use some decent size aluminium bar for the extension and use it to house the bearings. Convenient as you can do it all on a lathe.

Is it convenient to add another (e.g. 6201) bearing at the driven end of the screw? I'd prefer to have the screw supported with two bearings at one end as otherwise I suspect the significant radial force due to the tension of the timing belt will tend to bend the screw about the single angular contact bearing. Might be negligible in reality as clearly it works for Robin without ... ?

Good, only one small mistake. You only leave a gap on the left hand side, the tension end. On the right you want the 12mm nut to grip the angular bearing inner ring against the step in the screw. That gives you something to tighten the nut against so it stays where you put it. Don't want that right end nut free to unscrew itself.

The gap on the left only needs to be long enough to stop the 16mm part of the screw ever touching the bearing. If it does touch then the Belleville washers stop pulling on the screw.

My handle fitted inside the saddle, if it didn't I would have extended it. My X motor didn't fit so I extended that end a long way.

The extension can be as long as you need, it doesn't have to be wide.
A wide extension could get in the way of the motor. Allow room for the motor, you don't want the motor hitting the saddle or getting in the way when you want to turn the handle.
The extension has to take a big axial load from the Bellevilles.
The radial load is the motor torque.
The side loading is ordinary workshop bumps and knocks.
It has to hold the bearing square, otherwise the screw will flex when you turn it.
It is comforting if the extension carries any motor heat in to the bed, so the screw doesn't warm up.

A good tip here is to also if you are going to use the machine manually is to be able to disconnect the motors from any circuit. Otherwise they will act as little generators sending a nice bit of current back to your circuit boards :whistling:

Quote:

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Originally Posted by 2e0poz

they will act as little generators sending a nice bit of current back to your circuit boards :whistling:

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Have you actually had a problem with that?

If you short out a stepper coil you get a definite resistance when you try to turn it.

I don't feel any resistance or cogging when I turn a motor with the driver OFF or FREE so I don't think there is any electrical path for it to push against.

OTOH I could be delusional, it happens at my age.

Ezecnc Roger had this issue when he converted his viceroy, he did not suffer any damage luckily but did have a huge issue with resistance. Made it hard work to mill by hand. He was using large steppers but goes to show that the issue is there no matter what size steppers you use. It would be worth whipping out the DTM to check on any back current flow?