Homann Designs TM20LV (BF20,G0704) conversion

[phomann]

Hi Peter,

Thanks. At the rate I'm going, I think this will be the slowest conversion in history.

Cheers,

Peter

[Neptunes]

Hey haha I know what you mean projects come spurts of time between making a dollar, family, research and having energy. Keep it up looking good, it will sweet once done


Acoustic and Electric guitars and Basses. Repairs and parts
Neptune’s Guitars - Master Luthiers

[phomann]

Over the weekend I had a go at making the Table end plate for the X -axis. This is the plate that holds the floating bearing for the ballscrew. I figured that it was the easiest part to replace.

I took the original Sheetcam job I used to make the Corian end plate on the Taig mill and adjusted the feeds and speeds, the depth of cut and selected a 6mm slot mill to do the cutting.
There are eight holes drilled at 3.3mm that are to be tapped to M4. Four of the holes are to mount the bearing holder, the other four are to fasten a ballscrew end cover that I'll make at a later date.
The two slots are for the M6 mounting bolts and the counterbores are 5.5mm deep.



I cut the part outline to a depth of 8mm, then chamfered the edges before cutting out the rest of the outline. One finished, the holes were tapped and the edges cleaned up



It was then a matter of removing the Corian end plate, transferring the bearing over to the aluminum plate and mounting it onto the table.



So that's the first of about a dozen parts or so I need to make.

Cheers,

Peter

[phomann]

For my first cut, the quality of the cutting was fairly crappy. As I stated above I was using a 6mm slot mill. The depth of cut was 1mm, the feed was about 400mm/min and the spindle speed was around 2500rpm. Also, I was using mist cooling

There seemed to be too much vibration. The poor quality is clearly seen in the image below.



When I investigated I found that the Y-axis gib was loose. Loose enough to allow the table to rock when lifting by hand. Hopefully that explains what is going on. I did adjust them all at one stage but may have loosened it off at some point.

Hopefully the next part has a better finish.

Any advice on speeds, feeds, DOC and the like are welcome as my previous experience has been on my little Taig mill.

Cheers,

Peter

[Neptunes]

Hey Peter didn't realise corian was so strong in this application, looks clean cuts. I saw a few post back you were using the 2010 screenset and being seeing it a lot in my reading, would you recommend it for smaller CNC, worth the $20 US. The probing feature is what I really want.
Peter


Acoustic and Electric guitars and Basses. Repairs and parts
Neptune’s Guitars - Master Luthiers

[phomann]

The other thing to mention is that the spindle motor seems more than powerful so I'm sure that at some stage I'll use more aggressive cuts, once I sort out the finish issue.

Cheers,

Peter

[phomann]

Hey Peter didn't realise corian was so strong in this application, looks clean cuts. I saw a few post back you were using the 2010 screenset and being seeing it a lot in my reading, would you recommend it for smaller CNC, worth the $20 US. The probing feature is what I really want.
Peter


Acoustic and Electric guitars and Basses. Repairs and parts
Neptune’s Guitars - Master Luthiers

Hi Peter,

It's OK, but not that strong, but is very uniform, quick and easy to machine. Some of the parts were made 5-6 times adjusting them so as to line up with the mounting holes that had no accurate reference point to measure from. In fact yesterday I bumped into the Y-axis stepper mount and broke it. Mind you, it is probably the weakest part of the Corian bits I made.

As to the 2010 screenset, yes it is well worth the money. I primarily use it for the probing routines.

Cheers,

Peter

[Neptunes]

We use to use it on lots of industrial kitchen bench tops many years ago and it reminded me I have a 1200 x 1000 sheet under the house might drag it out and machine some jigs out of it for guitar. Was going to use 12mm lexan but that's cheaper and free .
I think I will grab a copy of 2010 and have a play, do you use the double probing feature from the videos it looks very handy for tool changes.
Peter


Acoustic and Electric guitars and Basses. Repairs and parts
Neptune’s Guitars - Master Luthiers

[phomann]

Hi Peter,

No I haven't setup the double probing for tool changes as I have nowhere to mount the fixed touch-off plate.

Cheers,

Peter

[phomann]

I managed to make the other end plate for the X-Axis over the weekend. After the issues I encountered last time, I made sure that all the gibs were snug and properly adjusted.

Needless to say the cutting finish was a lot better this time. Below is an image showing the cutting process.




When I went to change the end plate over I struggles to get the nut off then end of the ballscrew. Some of the loctite may have ended up on the ballscrew thread. I tried locking the axis but that was just putting all the pressure onto the ball nut which did not seem to be a good idea.
In the end I made up a clamping brace to hold the ballscrew.

The brace is a 20mm x 30mm aluminium bar about 400mm in length. I drilled a 3/8" hole to fit the ballscrew shaft, cross drilled with a 4.2mm drill for a M5 thread. I then cut then slit, drilled the 5mm clearance hole for the clamp bolt. I then drilled and tapped for a M4 bolt to tighten up against the shaft flat.

The nut then came off without a problem. It was well worth making and I'm sure I'll sure it a few more times. As can be seen in the last image I used the clamping bar to put the nut back on after the end plate was replaced.



Once the nut was off, I transferred the FK bearing block over and reinstalled everything.



Cheers,

Peter

[phomann]

And now for the sad part.....


I measured the backlash on the X-axis and it is 0.12mm.

So I have a bit of diagnostic work to do. when stepping with 0.01 increments, the dial gauge moves 0.02 on the first step and then 0.00 on the next. This pattern repeats it self. It's like the momentum of the first step moves the nut off the side of the screw that is pushing it, and on the 2nd step the screw catches up with the nut.

Another possibility is that the Fixed FK12 bearing block has some movement in it. I guess I could try pushing the ball screw back and forward. That may give me a clue.

Then there's always the belt drive to consider, although I think that this is the least likely cause of the backlash.

I've always planned to get double nuts for the machine, now that they are available but I want to isolate the source of this backlash first.

If anyone has experience with the FK12 bearing blocks or suggestions on how to go about this, I'd appreciate the help.

Cheers,

Peter

[pippin88]

Those bearing blocks often require shims between the bearings

[phomann]

Those bearing blocks often require shims between the bearings

Yeah, that what I thought. I think I remember Rocket Rod discussing it a while back.

Cheers,

Peter

[phomann]

Hi,

I'm looking at replacing the ball nuts on the ball screws with double anti-backlash nuts. The Screws and nuts were purchased from linearmotionbearings2008 and are the common RM1605/RM2005 ones.

Has anyone replaced just the nuts, or is it necessary to purchase them as a set?

Any advice or experience welcome.

Cheers,

Peter

[paul3112]

Hi Peter,

Both Nigel and Micheal have converted their mills to ballscrews
Nigel has fitted oversize balls to take out backlash on old screw/nut.
Maybe a chat with Nigel could be informative.

Paul

[phomann]

Hey Paul,

Thanks for the reply. I can rock the ballscrew back and forth about 15° - 20° without any movement on the axis so I need to do something.

Cheers,

Peter

[paul3112]

Hey Paul,

Thanks for the reply. I can rock the ballscrew back and forth about 15° - 20° without any movement on the axis so I need to do something.

Cheers,

Peter

any endplay on the screw? as in adjustment of fixed end bearings?( they only go in one way )
Products

[pippin88]

Peter, I bought double nuts from chai to retrofit - however I haven't actually fitted them yet (at least a year later...). So yes you can buy them separately. Do they work - don't know.

Suspect some adjustment of the spacer between the nuts may be needed for retrofitted ones.

[phomann]

any endplay on the screw? as in adjustment of fixed end bearings?( they only go in one way )
Products

Hi Paul,

I've checked the bearings and I put them in correctly. I'm fairly confident that it is in the ball-nut. I made a small loop program that moves the axis back and forth between 0.0 and 0.14mm and the dial gauge is dead still .

Cheers,

Peter.

[phomann]

Peter, I bought double nuts from chai to retrofit - however I haven't actually fitted them yet (at least a year later...). So yes you can buy them separately. Do they work - don't know.

Suspect some adjustment of the spacer between the nuts may be needed for retrofitted ones.

Thanks for that. I think I'm at a stage where I will need to order some nuts.

Cheers,

Peter