Homann Designs TM20LV (BF20,G0704) conversion

This is the start of a journey. I've had a Taig CNC mill for over 10 years now and it is a fabulous machine. I was after a larger machine and the Grizzley G0704, BF20 or Sieg X3 seemed popular choices.

If all turns out well I'll should be able to provide a nice controller kit for this type and size machine.

The G0704 is not available in Australia. The X3, is as are a number of BF20 style machines. In the end, I chose a TM20VL from Titan Machinery. It looks similar to the G0704 and the BF20L but does have some differences. I could have got a BF20L for less, but I was not sure of the quality. Also I wanted an R8 spindle so I could use TTS tooling.

I'm planning to do the conversion following the CNC Conversion DVD by Hoss. Obviously it depends on how closethe machine is to the G0704.


The TM20VL has the following Specifications:

• Spindle taper R8
• Spindle travel 50mm
• Quill diameter 60mm
• Table size 700mm x 180mm
• Table travel (longitudinal) 550mm
• Table travel (cross) 180mm
• Max. dist. spindle to table 360mm
• Max. dist. spindle to column 185mm
• Machine depth 580mm (to front handle)
• Machine height 930mm(head fully extended)
• Machine height incl stand 1730mm
• Head tilt 90º both ways
• T-slots 3 slots, 10mm studs
• Range of speeds 0-2500 RPM
• Motor 800W BRUSHLESS DC, single- 240v single -phase

I picked up the machine from the shipping depot. I ended up using a scissor jack trolley to get it off the trailer. I raised the trolley to the height of trailer and shoved, pulled etc.

A few pics below.

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.

Yeah that's different, looks like a new top plate with the bearing mount for a ballscrew might be in order.
Hoss

Hi Hoss,

Yes, I think that will be the way to go. I took a few photos of the X/Y ballscrews. They are 25mm diameter. The X screw nut mounts differently to the G0704 ones. You can see that in the photo. Hopefully there will be enough room

I also took of the left endplate from the X-axis. There is no bearing race, just a hole as a sleeve. A bit disappointing.

I'll make new endplates and I think I'll use this style of ballscrew supports.
1 set Fixed Side FK12 and Floated Side FF12 Ballscrew end supports CNC DIY | eBay

Cheers,

Peter.

Ok, I removed the table to see what is underneath. Below is what I've found.

The X Nut is quite interesting. It is low profile which is not good. The screw is 25mm diameter so there is only about 35mm clearance.

The nut has backlash adjustment. There is a 3mm ball bearing sitting in the nut. As the backlash adjustment screw is tightened the ball is forced against the screw.

Cheers,

Peter

Removing the saddle to look at the Y nut was next.

You can see the nut mounted to the back edge of the saddle. You can also see the bolt that holds the nut to the saddle.

With the saddle removed, you can see the gap through the base. Lots of room for the Y-Axis. :)

The Y-nut is interesting and has the same ball bearing backlash adjuster. The hole for the screw seems off centre but preliminary measurements indicate that it is on the centreline of the mounting boss.

Cheers,

Peter

So, now I need some help on how to do the X-axis ball nut.

I plan to make new end plates for the table which will hold the ball-screw end mounts. At this stage I'm planning to use 1605 ballscrews and use the FK12 and FF12 style ball screw supports.
FK12 16mm BALLSCREW END SUPPORT BEARING BALL SCREW CNC | eBay

I also plan to use a FK12 on the Y-axis as well.

The ball nut mount is more problematic. The ball nut mounts are 25mm apart so I could use them . The centreline of the lead-screw is 15 mm above the base and this is where the problem is going to be I fear.

I have a Taig CNC mill, and the TM20VL saddle will fit if machining is necessary.

The dimension of the Ballnut from CNCShop is attached.

The diameter of the ballnut is 28mm excluding the mounting flange. This gives me a 1mm clearance to the 15mm centreline. I could mill a clearance slot in the saddle for the flange. I would then have to mill the top of the flange so that it does not interfere with the bottom of the table.

I could also mill the top and bottom of the flange which is my preferred plan at this moment.

Any ideas welcome.

Cheers,

Peter.

You will not be able to machine the nuts on a taig. You can use some form of abrasive cutter (dremel stuff) if you have a high speed spindle in the taig, or you can just attach the dremel to the taig.

You could also use a bench/angle grinder and do it by hand.

Thanks, I should have realised it would be hardened. I'll see if I can get linearmotion2008 to do it when I order them.

Cheers,

Peter

Still sorting out how to do the conversion.

Both the X and Y nuts are screwed in place. The Y even has a boss that fits into the saddle so no adjustment can be made at all.

The X and Y end pates also have locating pins so there is no adjustment available there. I wonder if the threads are cut in place using a special tap that uses the end plates as an alignment jig. Anyway, it doesn't help me.

The G0704 mill retains the nuts by having the nut holder sit in a slot and two screw jam it in the slot once everything is assembled.

On my mill, the x nut is mounted with 2 screws that can't be adjust once assembled as the table sit over it. The only was I can see to adjust it would be to not fully tighten the screws, assemble the axis and allow the nut to self align then take the table off and fully tighten the nut screws. This sounds unlikely to work or be very easy to do.

The alternative may be to cut a slot into the saddle and change the mounting method similar to the G0704.

Whichever way it goes, I don't think it will be simple.



Cheers,

Peter.

I went out to the shed and had a better look at the saddle. It appears to be too low profile to use the G0704 nut holder mounting method.

The current X axis mount screws into 2 threaded holes in the saddle. one possibility will be to drill 2 new mounting holes (so as not to destroy the old ones) with the nut holder having matching threaded holes. The 2 holes in the saddle could be oversize to allow adjustment.

The X-axis could then be assembled onto the saddle, without the saddle being mounted onto the base.The assembly could be flipped upside down and the X-nut mounting adjusted and tightened.

Cheers,

Peter.

The Y-axis mount is located via a boss. There is no alignment adjustment in that method.

I could get some alignment capability in where the nut mounts to the nut holder by using smaller mounting bolts or enlarging the mounting holes. Sounds like a hack though.

Initially I'll just try to make an accurate mount and see how I go.

The nut is mounted at the rear of the saddle. The screw is only fixed at the front of the machine so at the closest point the nut is some 6" from the screw mounting point. so a minuscule od misalignment may be tolerated.

Cheers,

Peter

OK, I think I understand how they are doing the leadscrew alignment.

Attached is an image of the base where Y-axis bearing mount attaches. As can be seen there are the 2 threaded holes for the mounting bolts. There are also 2 holes that alignment pins are mounted into. You can see that on the 2nd image.

I believe that the bearing mounting plate is nudged around until the bearing block, leadscrew and nut are aligned. Then the bearing block is tightened and then the holes for the alignment pins are manually drilled and the pins inserted. If you look at the pins and holes, they are not symmetrical.

I should be able to do the same, drilling new alignment pin holes. Or, maybe the pins aren't needed?

Cheers,

Peter.

I'd personally skip the pins. You will have to realign every time you assemble though.

My plan for the conversion was to use belt drives, primarily so that I could tuck the motors away, rather than sticking out the ends. With the low profile saddle and the way the table ends can move right up to the saddle, there is too much work to ensure that there is clearance for the motors.

So, I'm now looking to direct drive the axes. I'll see if the bdtools conversion kit can be used. If so, I'll use that. That said, I think there will be too many differences.

I'm also not sure how important the alignment pins are. Obviously they are needed for mounting repeatability. They may also be need to stop misalignment if things are bumped, etc.

For the Y-axis I can't reuse the alignment holes as I don't know the locations. I may need to drill new ones by having holes at known locations in the bearing support plate, then using them as guides for drilling into the base.

Any advise welcome.

Cheers,

Peter

Quote:

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Originally Posted by 691175002

I'd personally skip the pins. You will have to realign every time you assemble though.

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Yes, that's what I was thinking. Hopefully it wouldn't be too often.

Cheers,

Peter.

Peter,
On my RF31, there are no alignment pins. Never has been and like you say, it has to be aligned each time. However in ten years or so, I haven't had to do that more than a couple of times. Also, the original lead screw nuts look exactly the same as my RF31 did. When I made my X axis one I kept having a problem with the two bolts not holding the nut mount tight enough and it would work loose causing backlash. For the nut mount, I used a couple of alignment pins and haven't had a problem since.

Quote:

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Originally Posted by phomann

OK, I think I understand how they are doing the leadscrew alignment.

Attached is an image of the base where Y-axis bearing mount attaches. As can be seen there are the 2 threaded holes for the mounting bolts. There are also 2 holes that alignment pins are mounted into. You can see that on the 2nd image.

I believe that the bearing mounting plate is nudged around until the bearing block, leadscrew and nut are aligned. Then the bearing block is tightened and then the holes for the alignment pins are manually drilled and the pins inserted. If you look at the pins and holes, they are not symmetrical.

I should be able to do the same, drilling new alignment pin holes. Or, maybe the pins aren't needed?

Cheers,

Peter.

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Your exactly right about the order/proccess for installing new pins. Infact not being symetrical may even have some benifits in stability ( but maybe not, but its not important). One thing the none symetrical pattern of pins does do is help you to know which end plate goes in which possition. With a odd pattern there is no question as to where each piece goes.


I would add the pins after making your alignment. Bolts work loose to easy and flex/slipping happens very easy. Thats not to say that with carefull alignment and tightening of the bolts it will not hold as needed, but if it did move just a tick and this was not enough movement so that it was noticed by the operator
then the screws/parts would be getting used while out of alignment. Ofcourse this could accelerate wear, and even cause possible problems with the accuracy which may not get noticed until something is warn, or after a 1000 parts where made incorrectly.


So in simple terms it is just much safer, plus anytime you tear the machine apart it will go back together much easier/faster. This is the way you want the machine, this way its an easy job to jump in and do inspections or ajustments. You will be more willing to do so if its easier. And anyway, its not hard to drill a couple of anywhere you want them holes for the pins. A tappered reamer for the pin size will be needed, but these are cheap. Plus once you get in the habit of using pins on assymblies they will hold up better (other parts/projects). I like the pins with a center hole drilled and tapped for using a screw/slide hammer to pull them back out when needed, another "it makes it easier" in the end kinda thing when it comes time to dissasemble the parts.


Jess

I fail to see how the alignment pins save any significant amount of time on re-assembly. You simply leave the bolts loose, run the axis so the ballnut is as close as can get to the bearing support, then tighten up the bolts. It takes no time at all.

Regards,
Ray L.