Homann Designs TM20LV (BF20,G0704) conversion

[phomann]

Hi Peter,

I think it is a good 1/2 -1" above the Y-axis ways. If you look at the mounting plate, the motor centreline is above the X-axis screw.
I am on holidays camping at the moment and will take some photos when I return on the 12th. (As you can see by the TV antenna, the camping is not too rough )

The corian seems strong enough to allow me to do do a bit of machining on the mill. I've test run both the X and Y axis. and even test run the Y-axis with a servo setup.

My plan is to make the aluminium conversion parts on the mill itself and replace the corian parts with the aluminium parts as they are made.

I'm doing this as the only other mill I have is a Taig cnc mill, which would cut the aluminium albeit a bit slow and stressful for the Taig.

Cheers,

Peter.

[phomann]

Over the weekend I had a bit of time to work on the Z-Axis ballnut holder.

It is made in 2 parts as shown below for easy assembly into the column. The plan is to;

1. mount the lower cube part onto the ballscrew nut
2. then insert the ballscrew into the column
3. Attach part 2nd part of the nut holder to the first
4. Mount the nut holder to the Z-Axis slide

[phomann]

The two parts need to lock together so I decided to make a square peg that locks into a matching square pocket.

The first job was to make the square peg. The part is made out of 50mm x 25mm aluminium stock. The peg dimensions are 25mmx 20mm.

The material (15mm) either side of the peg was removed on my Taig mill. and the peg was then reduced so it was 12mm tall.

Two clearance holes for the 6mm capscrew mounting bolts were drilled.

The part was then flipped over and the holes were counter sunk for the mounting bolts.

[phomann]

As depicted in the images below part A of the Z-axis ballnut contains a pocket for part B to lock into. The two parts are held together with a pair of M6 bolts.
Part A is attached to the ballnut with 4 x M6 bolts. The block is 50mm x 50mm so two of the 6 mounting holes are not used.

[phomann]

The first image shows both part A and Part B of the Ballnut holder. I was very happy with the fit of the peg into the pocket. It ended up being a firm press.

The next two images show the two parts bolted together.

[phomann]

These images show the nut holder mounted to the Z-nut on the ballscrew.
The last of the images shows the ballscrew clearance through 25mm hole in the nut holder.

The hole was drilled with a 25mm drill bit on the drill press.

[phomann]

These two images show the Z-axis ballscrew and nut holder inserted into the column.

I'm really pleased with how it turned out as it is so quick to assemble the axis.

[phomann]

I still have a bit of work to do with respect to making the Z-axis top plate that holds the Z-axis bearing supporting the screw. It's going to be tricky as there are no real reference points.

The column originally just had a thin sheet metal cap covering the top of the column as the original Z-axis was supported by a right angle bracket mounted to the side of the column that contained the crown and pinion gears plus the screw.

You can see how the poorly the holes holding the top plate were drilled. I'm thinking of filling them with cold weld filler before I drill any new holes.

Unless anyone has any recommendations.

[phomann]

My plan for the top plate is to make a replacement plate for the side plate. This will be made from of 12mm aluminium plate.

I'll then make the top to sit on the top of the column. It will bolt to the column in the 4 corners of the column where the original top plate bolted to as there are welded gussets already in place for this.

Initially it will be bolted to the new side plate with 2 bolts as well as to the Z-Axis Dovetail section with another 2 bolts. I then plan to drill the 4 holes for the corner bolts.


The top plate will have all the holes CNC machined so I plan to use them as a guide when drilling the holes into the top of the column.

As with most of the parts I've made for the conversion, I'll make them out of 12mm Corian first.

This is going to be especially useful for the top plate as I expect a little trial and error in getting the location of the Z-axis bearing block hole into the correct spot.

The top of the dovetail slide will be a reference. I need to determine the gap between this and the surface on the underside of the Z-axis slide that the nut holder bolts to. Once I know this I should be able to determine the distance to the centre of the ballscrew based on the ballnut holder dimensions.

I then need to determine the centre of the slot in the column. Theoretically, this should be where the hole in the top plate needs to be. In the image you can see the marker lines where the centre should be.

I'll make the top plate, fit it, measure any misalignment, make another out of corian and refit. Hopfully the 2nd one should be spot on.

Once it is done, the final top plate will be out of 20mm aluminium plate.

If anyone has suggestions on making the top plate now is the time to speak up.

Cheers,

Peter.

[Mad Welder]

Nice progress, good photos...

....... I expect a little trial and error in getting the location of the Z-axis bearing block hole into the correct spot......
Cheers,

Peter.

You've a good thought process....when I was making my Z axis ballscrew mount I was scratching my head for a bit before I realized the reason for Optimum's fore and aft sliding leadscrew mount, and after also machining my first ballscrew nut mount too small.

(If you already explained the following earlier my appoligies) here's a little explaination for those looking to purchase similar mills to ourselves, the reason that one cannot use the stock leadscrew nut dimensions to make the new ballscrew nut mount is that the manufacturers allow for easy removal of the Z axis saddle without taking off the top plate of the Z axis and the 90degree manual rotation wheel....when you remove the spindle head off of the Z axis saddle you then only have to remove two allen hex head bolts which hold the stock nut in place and then you can push the nut back towards the rear of the mill colum as there's a machined resess in the saddle, and then the saddle is free to slide down or up and off the colum.....hope I haven't confused anyone more here!

and Peter you're bang on track with your analysis, and I did pretty much the same after figuring out the reason for the sliding stock nut mount....so in my case using the face of the Z axis saddle's taper as my referance (Datum) point all I did was measure with my digital verniers the distance from the back of the resessed slot on the Z axis saddle to my datum point and then to the centre of the stock leadscrew as in my case I used the stock top plate.. so in your case (depending on your chosen location of the ballscrews position in the colum i.e. off centre etc.,) be as straight forward as that for you too..

[phomann]

Hi Eoin,

Thanks for the comments. I gives me confidence that this may all work out. Although I haven't seen any information on Converting a TM20VL machine, most of what I've done is from gleaning the techniques others have used in converting similar sized machines.

I still haven't decided whether to put slots into the top mounting plate, or do the first one, then make a 2nd using the errors in the 1st as reference. It doesn't take long to whip on out of corian.

Cheers,

Peter

[phomann]

Well it's been quite a while since I last worked on the conversion. I must be 10 to 12 months. Every time I walk past it in the shed I feel a small guilt twinge.

I haven't really done much, but at least it is a start.

The images below are the side cover, that replaced the crown and pinion gear bearing that came with the mill.

I first made the part out of Corian to test the fit. As there are no drawings, I have to measure then guesstimate what the correct dimension should be. As an example in point, there is a radius on one corner of the plate. I used drill shafts to determine the radius. All the machine dimensions up to date appear to be metric, so I've confined myself to that. A 12mm drill shaft seemed to fit the radius to I went with that.

As can be seen it is a good fit into the radius.

Once I test fitted the Corian piece, I decided to make the final aluminium piece as well as the top plate will need to bolt to this. Note, the Corian piece is out of 12mm thick stock whereas the aluminium piece is out of 10mm stock and fits flush.

I've just about finished drawing the top plate although it is difficult to get the reference point right. I expect it to have to take 2 or 3 Corian prototypes to get this piece correct

Cheers,

Peter.

[phomann]

Hi,

This images shows the difficulty I'm going to have attaching the top plate. The original top plave was just a thin sheet steel cover. The mounting holes were just hand drilled.
I'm thinking of filling the holes with JB weld as some of the locations are less than ideal.

I'm planning to use two bolts int my aluminium plate, another two bolts into the dovetail way, and two on the right hand corners.

That said I'm still mulling it over.

Unfortunately, the column is too hight by about 150mm to fit into my pedestal drill.

Cheers,

Peter

[arizonavideo]

Its more important that the top is flat than where the holes are. Just use the stock holes and spend more time shimming the plate flat. It takes a long time to get the ball screw square and true in the column. I would just trace the hole pattern and make the part.

[phomann]

Hi arinonavideo,

Thanks for the advice, I appreciate it. The holes are only for M3 bolts so I'll need to upsize them but I agree that getting the top plate level is critical.

Cheers,

Peter

[pippin88]

Peter,

Great to see some progress.

I've got bits and pieces done on mine but limited time is always the issue.

The Y axis is coming along.

Once again it is measuring the sizes and mounting locations by measurement. What I doing is taking measurements with vernier callipers, then with the understanding that it is a metric machine and assuming that the dimensions are in metric, round the measurement to a reasonable values based on what I feel an engineer would have chosen.

So far it has worked out pretty well. The X_Axis end plates were spot on, The mounting holes for the plate were 160mm apart. The ballscrew centreline is 50mm below the mounting hole centreline. The ballscrew centreline is 15mm above the saddle, etc.

The Y-nut holder has a 15mm boss that locates into the saddle and is held there by a M8 capscrew. The original parts can be seen below.

Just a correction to this post. The Y Nut holder is held on by an M6 screw. I ran into trouble because I made my mount for an M8 screw (had to make mount before I pulled mill apart). My error meant I had to drill out the saddle hole to 8.5mm, and turn down the bolt head to fit the 11.3mm clearance hole.

Cheers,
Nick

[phomann]

Hi Nick,

Sorry about that.
Cheers,

Peter

[pippin88]

Hi Nick,

Sorry about that.
Cheers,

Peter

Peter,

Not your fault at all. Your thread and drawings have saved me many hours.

I managed to get the X and Y Ballscrews and mounts all done. On my mill the central Y slot is off centre (or the y nut mounting position is) and quite uneven / bumpy, which meant I had to laboriously file the bumps to widen the slot a bit.

Look forward to seeing your approach to the Z axis mounting. I've got quite a ways to go to catch up.

Cheers,
Nick

[pippin88]

The first thing I noticed is that the TM20VL Z axis is different from the G0704. The latter have a plate with the bearing to support the Z-axis screw. The TM20VL just has a sheet metal cover.

I popped the cover off and it is quite different. The screw support is beneath the crown and pinion gear

The bearing support is on a plate that also has the z-axis handle. You can see the setup in the photos.

Cheers,

Peter.

Someone might find the following of use if converting this mill:

I spent the afternoon pulling apart the Z axis. Head and carriage came off fine.

Then I tried to get the side plate out that holds everything in place.

Peter's photo is of interest:
http://www.cnczone.com/forums/attach...ion-z-axis-jpg

Mainly because my mill only had 3 bolts, with no bolt in the top left area (and no hole).... or so I thought.
The three screws came out fine, but I couldn't get the alignment pins out. They are threaded for a removal tool, I was using a bolt and pulling on it - nothing.
I then proceeded to remove all the bondo and paint between the column and this plate, which is quite a large amount - big gaps. I tried a bit of hammering from the back (through the top of the column) - nothing. Then I proceeded to drill the alignment pins out as deep as I could but couldn't drill the quite the full depth of the plate.

With some more hammering I got one edge to open up, drove a wedge in all around. Got a far bit of separation on the right side and lower left, but the upper left still seemed to be attached. By this time, with all the hammering and wedging, I've broken some of the cast iron plate edges and a small round shape becomes visible in the top right of the plate. There is a bolt in there. The sneaky ******** bondo-ed and painted over a bolt, that is a bit lower and not in line (not in the square pattern) with where it should be (and where the one in the photo above is). There is a tapped hole in the column where you would expect a bolt, and where Peter's has one. Not sure what they were doing...

Hopefully haven't done any damage to the column with all the hammering etc...

[phomann]

Yes, I removed quite a bit of bog as well. Luckily the bolts were where they were meant to be. You can see the pins in the first images.

I did a bit of work on the Z-Axis top plate today (I have been working on it for a couple of weeks). It's been by far the most difficult part to convert. As the top of the column just has a tin sheet metal cover there is no reference point for the Z-axis bearing. I measured it as best I could and got it close. Then by installing the plate and measuring the error I made another and test fitted that. I just finished version 7 this afternoon.

I then drilled the mounting holes for the top plate. I made a couple of guide plates to try and keep the hand drill square as the column was too large to fit into the pedestal drill stand. I locked the Z slide in place, then tightened the screw up against it, using a couple of shims to keep the plate square.

Attached are a couple of photos showing the installation.

With a bit of luck I might get the the motor bracket done before the weekend is done.

Cheers,

Peter.