[phomann]

Yes....

I drew up the dxfs for the table X endplates last night and ran them through Sheetcam. Over the weekend I'll make them out of 12mm Corian.

I plan to assemble it first the Corian to check that all the dimensions are correct first before cutting it out of 12mm aluminium. Corian cuts very easily and it will be relatively quick to re-cut them on my little Taig mill if necessary.

I should be able to used these endplates to assemble the X-axis set up the X-axis nut holder, which will be my biggest concern at the moment.

I'm using these ballscrew bearing blocks.
FK12 16mm BALLSCREW END SUPPORT BEARING BALL SCREW CNC | eBay

I haven't see anyone else use these on a conversion yet, and wonder why as they make the assembly a lot easier and quicker. My guess is that they are a little expensive, but in the scheme of things it is not too bad.

[691175002]

I wouldn't trust them unless they can provide some real bearing specifications. They claim a matched "C7" pair but C7 has no meaning for ball bearings.

[phomann]

Hi,

The ones I have are sourced from Taiwan SYK-?????????? SONYUNG Industry Co.,Ltd-Ballscrew Support Unit,Nut Bracket,Motor Bracket

Many of the ebay units are Chinese copies, and have a different cover over the bearings.

Anyhow they seem nice in the hand, but time will tell once they are installed.

BTW the manual states that the C7 refers to the applicable ballscrew accuracy grade.

Cheers,

Peter

[phomann]

Last night, I made a prototype end plate for the X-Axis.

I drew it up in DraftSight, then loaded the dxf file into Sheetcam and created the G-Code.

The end-plate is cut out of 12mm Corian. I used Corian, as it is easy to cut, yet stable enough to be used to check the alignment etc. I'm even considering that I may be able to use the Corian endplates on the mill to allow me to cut the final plates out off 12mm aluminium, rather than cutting them on my Taig mill.

The holes for the 6mm cap screws that fasten the end-plate to the table were drilled to 6mm, so it is a tight fit. I did this to see how accurately the holes in the table were drilled. The bolts fitted up very well, so they may have been machine/jig aligned and drilled. This is in contrast to the locating pins which were obviously hand drilled as the holes are not even perpendicular.

Later on it may be necessary to increase the clearance on these holes so that some slight adjustment is available. That is also the reason that the countersink diameter on these holes is quite large.

If you notice the fit, the top of the side plate is slightly below the table sides. I'm not sure what this means in terms of fit. When I measured up the original plate. The lead screw centre appeared to be 50mm from the top of the plate, and the mounting holes appeared to be 25mm below the top of the plate. The mounting holes were 160mm apart. These were the dimensions I used as I figured that the mill was built of a blueprint somewhere and it was logical to use these dimensions.

The FK12 bearing block is held in with four M4 bolts.

I also put in four holes tapped for M6 bolts. These will be used to mount the plate that will hold the stepper or servo motors. The plate will have elongated holes that will allow me to tension the timing belts. There are holes either side of the centre as I haven't decided yet which side of the table I'll be mounting the motors.

The next step is to make the plate for the FF12 bearing block. It requires a slightly smaller hole.

[phomann]

One thing I'm thinking of changing is to change the mounting of the FK12 bearing block from the other side. That way the inside of the flange will line up with the end of the table and the ballscrew length needed will not be dependant on the thickness of the end-plate.

That way, it would not matter if the end plate material was 12mm or 1/2" plate.

[phomann]

I tried putting the bearing block on the inside but there is not enough clearance to the underside of the table. It's probably less than 1mm but I think I'll just leave them on the out side.

I also made up the other end-plate for the floating bearing block.

It's almost time to order some ballscrews .

I'm not sure on what diameter to have on the end for the timing pulleys. I am tossing up between 10mm, 3/8" or 8mm.

At this stage I'm thinking of getting 3/8" as there seems to be a better range of XL pulleys and also the stepper shafts are 3/8"

Cheers,

Peter.

[phomann]

I'm still not completely decided about the X axis ball nut mounting method.

I could cut a slot in the saddle and mount it like the G0704. The only issue that concerns me is that the saddle is only ~10mm thick where the slot will be made.

That would mean that the bolts that jam the holder in place would have to be M4 or M5 bolts.

From experience is this going to be sufficient?

Cheers,

Peter.

[phomann]

I've been working on ways to mount the Y-axis belt drive set-up and motor. Attached is an image of my planned layout.

Dos anyone have experience on using a such a long belt (XL) as I'm concerned that it is too long. The length is needed so I can tuch the motor out of the way, rather than it sticking out the front.

The idler bearing is set quite low so that I can use a smaller pulley on the motor and get a 2:1 ratio.

Cheers,

Peter

[Bubba]

Peter,
On my RF31, my Y servo is located below the center line of the Y screw and uses an adjustable motor mount to maintain tension on the belt. It C-C distance is variable from about 9.4" (~238MM) to about 10" (254mm) I also use an XL belt and except for the time that I ran into a hard stop (before limit switches) at full rapid and the "fuse" was the belt, I have had no problems. In my case, the pulley ratio is 1.4:1 (18:26 teeth) if that makes any difference and I used no idler to gain more pulley wrap.

[phomann]

Hi Art,

Thanks I really appreciate the reply. The idler is there to clear the belt from the Y-Axis way more than anything else.

The mounts for the stepper will be adjustable to tension the belt. The pulleys in the drawing are 28 tooth. I'll end up with a similar ratio to you as I want the option to try servos. I don't think the machine needs servos but I want to design a BoB for the G320X drives, and this machine will do as a testbed.

Cheers,

Peter

[SCzEngrgGroup]

Peter,

You'll want more than 2:1 ratio for servos - they are usually reduced 3 or 4 to 1, both to increase torque, and to bring top speed down to a reasonable level.

Regards,
Ray L.

[phomann]

Hi Ray,

Yes, that is my concern. I may be able to squeeze 3:1 with a 10:30 pulley set, but there is barely enough room for the 30 tooth pulley.

The 10 tooth pulley would work with the servo 0.25" shaft and I may have to move the idler to get enough wrap on the pulley.

The way I've designed the stepper and belt plate, it is very easy to remove it and replace it with another.

In the end I'll probably go with the 570 oz.in stepper with a 20:20 pulley drive. I also want to try a 387 oz.in motor with a 16:24 pulley setup for a 1.5:1 ratio. That way I'll be able to use a G540.

Cheers,

Peter.

[phomann]

Attached are images for the ballscrew dimensions. I plan to send these to Chai from linearmotionbearings2008.

Before I send them off, can anyone see any errors or deficiencies with the drawings?

Cheers,

Peter

[SCzEngrgGroup]

Peter,

Coupla things.... Your dimensions should all reference a single datum, like one end of the shaft. Giving incremental dimensions as you have requires the machinist to do arithmetic, which invites errors. Also, your tolerances are odd - a dimension with two different negative tolerances? That's just weird. Should be either a range, or a value with + and - tolerances, one of which can be zero if you like.

Regards,
Ray L.

[phomann]

Hi Ray,

Good points. The tolerances I copied from the FK12 and FF12 data sheets. They are both negative as it needs to be under size for the bearing fit.

I thought that providing the nominal size of 12mm then the range of under size tolerance would add context.

But then, I'm no draftsman.

Thanks for the input.

Cheers,

Peter

[SCzEngrgGroup]

Hi Ray,

Good points. The tolerances I copied from the FK12 and FF12 data sheets. They are both negative as it needs to be under size for the bearing fit.

I thought that providing the nominal size of 12mm then the range of under size tolerance would add context.

But then, I'm no draftsman.

Thanks for the input.

Cheers,

Peter

Peter,

More likely to just confuse them, since the base dimension is not really metric to begin with. I would specify the maximum dimension, with a max tolerance of +0.00. That makes the intent very clear.

Regards,
Ray L.

[phomann]

Hi Ray,

OK, will do.

Cheers,

Peter

[hndswthtshdws]

There is an ISO standard for tolerancing different kinds of fits. In some cases it is proper GD&T to have double positive or double negative tolerances. This is most likely a sliding fit into the bearing (H7g6 fit).

Draftsmen and machinists know this. Its not at all uncommon.

In addition to using a datum as stated above, machinists appreciate it when all reading is horizontal.

Here is a ISO 268-2 tolerancing chart for different kinds of fits: Limit and fit | ISO hole chart | Tolerance

[phomann]

Hi,

I placed the order for the ballscrews yesterday with Chai from Linearbearingsmotion2008. I asked if he could supply extra balls. Chai said he would but in 100 extra ball for free.

I guess I'll see them next week some time.

The submitted drawings are attached for reference.

Cheers,

Peter

[pippin88]

Peter, what's the damage for the 3 screws? Interested as I may convert my TM20LV (long term)