Homann Designs TM20LV (BF20,G0704) conversion

[Fastest1]

Why the extra balls?

[phomann]

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

Under $200 including shipping to Oz.

Cheers,

Peter

[phomann]

Why the extra balls?

There has been some discussion about some nuts missing balls. Also in case I loose any.

Cheers,

Peter

[phomann]

I've been working on the X-Axis ballnut holder. I've finally realised that my mill is based on the RF series. That was what Hoss was referring to earlier on.Maybe it should be called an RF20.

It's slow going working on a 40mmx40mmx70mm piece on aluminium on my Taig mill.

The X-nut holder will be bolted from underneath as this is the only way I can see that the alignment can be adjusted for.

Also, because of the low profile and lack of headroom, the hole in the nut holder will only be 20mm to clear the screw. The nut will not pass through the holder but be bolted to it. I can do this as the nut holder is fastened to the centre of the saddle.

Cheers,

Peter.

[Fastest1]

How do we know how many were supposed to be in there? Also dont take them apart if you dont have to. I did discover if you take a piece of rubber tubing the OD being just smaller than the ID of the ballnut seal, you can push it against the screw and unscrew the nut onto the tubing and not lose any balls or if you just need to flip it around. Reloading the ballnuts is a PIA. My understanding of the quantity of balls has more to do with load carrying.

There has been some discussion about some nuts missing balls. Also in case I loose any.

Cheers,

Peter

[Fastest1]

Though it might seem a little nerve racking. You could cut the slots to install X and Y brackets like the G0704's very easily in your carriage. Probably easier than the alternate plan. It is a simple straight plunge. As long as you are either parallel or perpendicular to the ways you will have no problems ;-)

[phomann]

How do we know how many were supposed to be in there? Also dont take them apart if you dont have to. I did discover if you take a piece of rubber tubing the OD being just smaller than the ID of the ballnut seal, you can push it against the screw and unscrew the nut onto the tubing and not lose any balls or if you just need to flip it around. Reloading the ballnuts is a PIA. My understanding of the quantity of balls has more to do with load carrying.

No I don't plan to take them apart. It's more of a contingency than anything else.

[phomann]

Though it might seem a little nerve racking. You could cut the slots to install X and Y brackets like the G0704's very easily in your carriage. Probably easier than the alternate plan. It is a simple straight plunge. As long as you are either parallel or perpendicular to the ways you will have no problems ;-)

Ye, that's my backup plan. The web in the saddle is not very thick, 10mm maybe 12mm only. I wasn't sure if there was enough meat for the clamping bolts. I'm presuming they would need to be around M6 in diameter.

Cheers,

Peter

[phomann]

Attached is an image of the X-Nut mount. Just finished drill the clearance hole for the ballscrew.

The 20mm Drill bit make quick work of the aluminium.

Cheers,

Peter

[Fastest1]

That looks like it will work well. Are you planning to cut a slot in the top of the carriage so the mount can be moved a little for alignment?

[phomann]

No, it gets mounted in place of the nut in message 64. The net nut holder has 4 threaded mounting holes. The bolts come from the underside of the saddle. The bolt holes in the saddle will have a little clearance for alignment adjustment.

For the initial alignment, the table is laid upside down on a bench and the saddle with the nut holder bolted loosely to the saddle put onto the table. At this stage the nut and ballscrew have already been bolted to the nut holder.
The table end plates are mounted and everything is aligned and tightened.

Once aligned, the end plates are removed and the saddle slid off the table and the ballscrew and nut unbolted from the nut holder.

The saddle can then be mounted to the base and right way up and the table then mounted back onto the saddle.

Once I mount and align the nut holder to the saddle, I shouldn't have to touch it again. That said, I still have to do the Y-nut holder , so the X-nut holder may need to be removed to facilitate the making of this.

Once I take some photos of the X-nut holder it should be a little clearer.

Cheers,

Peter.

[phomann]

Well, I've finally made some progress. The X-nut holder is done. Unless I've made it a mistake.

The holder is 70mmx40mmx31mm. There is a 20mm clearance hole for the ballscrew to pass through.

The ballnut is attached via two M5x0.8 bolts. The holes pass all the way through the holder so I can put another ball nut on the other end if I feel that it is necessary to have a zero backlash system.

I accommodated the original nut's M6x1 mounting bolts. They are on a 50mm pitch. I plan to attach the holder with four M6x1 bolts from the bottom. That way I can adjust the alignment when the saddle is on the table.

You can see the centre punched marks for these mounting bolts in the saddle.

[phomann]

I was a bit worried about the clearance between the nut holder and the inside of the table. I shouldn't have been as there is a lot of room.

I installed the saddle onto the table upside down to test this, and also put on the endplate prototypes to see the fit. All I need now are the ballscrews to arrive and I can do a test fit.

You can understand why I want to fasten the holder with bolts from the underside. I plan to do all the alignment and adjustment of the X-Axis with the table on the bench like this.

As can be seen from the photos there is a lot of clearance. BTW, I need to get shorter bolts if you are wondering why they are protruding.

[phomann]

The mounting on the X-nut holder will have 6 bolts. I've seen some people pin the holder to ensure that it doesn't move.

Any comments on whether I should do this? And if so how is it done? I understand I seen to drill the holes through the saddle and nut holder while it is aligned in place, but I've noticed that some of the pins on my machine are threaded. Is this what I need to do? If so, where do I get these pins from?

The only pins I have are dowel pins. can I use these and press them into reamed holes and loktite them into the saddle.

At this stage I plan to try the machine without pins unless advised otherwise.

Cheers,

Peter.

[Fastest1]

I think you are over worrying about the alignment. Yes it is important but it looks like you did your layout pretty well. Test it as it is, if you run into a movement issue, solve it then. These little machines shouldnt be overpowering the bolts ability to hold before stalling. I thought about double ball nutting the screw as a method of minimizing backlash but if you have seen my video measuring the backlash of my linearmotion2008 ballscrews. There was less than .0005 in X or Y (much less than that, as I could barely see the needle move on an .0005 indicator). Z was just under .001. I did grease my ballnuts not oil if that made any difference. I figure if it came with Zerks fittings, they must want grease. After a few more hours of run time I will pull it all apart (do some more mods) and recalibrate and see where the backlash stands then. Btw good work and you are going to love the difference over manual!

[phomann]

Hi, thanks for the reply, I appreciate the advice.

Most of it is just extra planning in case it is needed. Once I get the Ballscrews, I'll see if I can just use the two original mounting holes. If not I;ll then use the 4 from underside.

Cheers,

Peter

[phomann]

The Ballscrews from Chai turned up a few days ago. All looks good.

The ballscrew end bearings all slipped on with a nice fit. I had to turn the nuts end for end on each screw to suit the way I'm mounting them. though. I'm glad I asked for the extra balls as I did loose two.

I took a quick shot of the X-axis ballscrew mounted onto the saddle.

When I made the X-nut mount block the centreline of the nut is 15mm from the top and 16mm from the bottom of the block. I did this as I wasn't sure if the screw centrline was 15mm or 16mm from the saddle surface.

From my measurements it seemed line it was 16mm. When I mounted it and put on the endplates it was obvious that 16mm was too high so I flipped the block over and it all lined up quite well. There is some ever so slight misalignment somewhere but that will be easily fixed by providing a little clearance in all the mounting holes.

I put on the end plates and used a power drill connected to the screw to run the saddle back and forth. It showed that the X-axis is going to work, so I'm very happy about that. Unlike the G0704 with its jam bolts, this mill does not have a nut mounting system that provides an alignment system. It all needs to be made accurately, which was not that easy since all the measurements had to be made and are not documented anywhere.

Cheers,

Peter.

[Fastest1]

Great to hear on the screws arrival. We all hooked our drills to our ballscrews in our impatience to see movement, those who don't admit it are lying or jaded. My understanding of the ball count is more related to load capacity. The backlash is determined by ball to race accuracy. I am not suggesting less just an observation.

[phomann]

An Overdue Update.

The X axis is basically finished apart making the final parts out of aluminium.

I'm planning to run the mill using the Corian parts, using the mill to make the aluminium parts.

The mill will be used to convert itself to CNC.

Below are the parts made and purchased for the X-axis conversion.

[phomann]

The first step is to screw the X-axis ballnut to the nut mount. As can be seen the nut itself does not go through the holder, only the ballscrew does that. This means that the hole can be smaller (20mm) and is just a clearance hole that can be drilled on a pedestal drill.