Thread: Homann Designs TM20LV CNC conversion

The following images show two of the three pulley set-ups I intend to try.

The 1st is a 20 to 28 teeth set-up giving a ratio of 1.4:1 using a 570 oz-in motor.
The 2nd is a 14 to 28 teeth set-up giving a ratio of 2:1 using a 387 oz-in motor.

I also have pulleys and belts for a 20 to 20 teeth set-up giving a ratio of 1:1 using a 570 oz-in motor.

I'm hoping that the 2:1 setup with the 387 oz-in motor will be adequate. That way I can use a G540 as the stepper driver. I think it will be Ok.

With this setup;

5mm travel per rotation of the ballscrew.
200 steps per revolution of the motor
2000 steps per revolution of the motor using a Gecko 10 microstep drive.
4000 steps per revolution of the motor using a Gecko 10 microstep drive and a 2:1 pulley ratio.

This ideally equates to;
A resolution of 5mm/4000 or 0.00125mm per step (0.0492 thousands of an inch)
An accuracy of 5mm/400 or 0.0125mm/step (0.492 thousands of an inch)

A 60ipm feedrate requires the stepper motor to rotate at;
60 ipm = 60*25.4 = 1524mm per minute

that is: (1524)/5 = 304.8 revs/minute

and with a 2:1 ratio 609.6 rpm

which is 609.6 *2000 /60 = 20,320 steps/sec

600rpm should be ok for the stepper but we will see. My taig mill rapids are set at 60IPM, so with the 20tpi leadscrew, the steppers are running at 1200 rpm. If it is in the torque delay area, the gearing will become less effective.

As to rapids of 60 ipm, I know there are lots of conversions that run a lot faster. For me 60ipm should be fast enough.

I really want to see if these mill conversions can be driven by the G540.

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.

For the new Y-nut holder, I used 25x40mm aluminium bar. It is just wide enough to slip down through the slot in the base.

Since the screw is 16mm compared to the 25mm one that came with the machine, the hole is the front of the base where the screw attaches to the bearing block has quite a lot of clearance for the new screw.

As the saddle extends a long way (40%-50%) over the front of the base I decided to take advantage of the smaller screw diameter and lower the new screw centreline by 4mm. This allows me to have more clearance and fit a larger pulley along with the pulley and belt cover without worrying about any binding resulting in reduced travel.

To make the Y-nut holder, I chucked the 40x25mm stock into the Taig 4 jaw chuck mounted on my 7x14 CNC lathe. Once the stock was centred, I turned the boss, drilled and tapped the M8 mounting hole.

While still in the chuck, I used the tool-bit to scribe the centreline down the side of the stock. This was to ensure that when the work piece was transferred to the mill I could easily locate the mounting boss centreline.

Once in the mill The centre hole and mounting bolt hole pattern was centre drilled. The bolt holes were then drilled countersunk and tapped for M5 bolts.

I then used a drill press to drill the centre clearance hole, stepping up in drill sizes until the 20mm hole was drilled.

Unlike the X-Axis ballnut which went smoothly, I had all sorts of chatter with the 20mm drill bit (previous drill was 1/2"), with the MT3 taper chuck holder dropping out of the quill, and/or jamming in the work- piece.

As you can see, I has to flip the ballnut over on the screw to mount it the way I need it.

Hi Peter,
When I have done mill conversions I drill off centre in the yoke and this allows you to allign the ballnut to each end. I am referring to the threaded hole in the round boss at the top of your photo.

Your photos and documentation are a good reference so thanks for the effort of posting. You have inspired me to start a hydrid that I have sitting around for three years. I had 10mm plates laser cut and have a 150mm square column with 5mm wall for the column. For your information for the stand I got two 8m lengths of 75 X 75, 4mm wall tube for $260 last week which I thought was a reasonable price for Perth.

Hi Rod,

Thanks for the input. I think I understand what you are saying and it would provide a cam action, but I don't think it applies here. The Boss on the nut holder is a tight fit into the hole in the saddle. The screw just holds it there.

I can get alignment adjustment from the bearing plate mounted to the front of the mill base. The holes are elongated to allow movement before the bolts are fully tightened.

I look forward to your build, as always I'm sure it will be inspirational.

Cheers,

Peter.

Would be interested in seeing the details of your 7x14 lathe at some stage Peter.

A bit more progress on the Y-Axis.

I made up the following parts for the Y-axis over the weekend.

• Bearing block support
• Spacer
• Stepper plate

The Bearing block support is made up of two 12mm thick pieces of Corian. When I make the "Real" piece out of aluminium, I'll use a single piece 20mm thick, or two 10mm thick plates. The FK12 bearing block is 17mm deep, so having the bearing block support 20mm thick will reduce the extension on the front of the machine by 4mm.

You can see in the photo showing the ballscrew that I've left the clearance to reduce the bearing block support thickness.

The Spacer will also end up being made from 10mm aluminium plate as well in the final version.

The stepper plate will eventually be made out of 12mm aluminium plate as well.

You can see from the photos that when the saddle is fully forward it projects right across the bearing block supports and stepper plate, with very little clearance. In fact you can see the saddle deflecting the belt

The photos show two 28 tooth pulleys as I messed up the belt lengths and I didn't have a belt the right length for the 20 tooth pulleys which I plan to use for a 1:1 drive.
Although 20 tooth pulleys will clear the saddle, they would not clear the inside of the cover that will fit over the stepper plate.

I'm thinking of trying 16 or 18 tooth pulleys for a direct drive. Hopefully there will be enough teeth in contact with the belt.

I also have plans to put an idler bearing onto the stepper plate to deflect the belt away from the saddle if I want to use the 28 tooth pulley for a gear reduction drive.

Cheers,

Peter.

I wired up a 387 oz.in motor on the X-Axis to a Gecko G540 with a 1:1 belt ratio using 20 tooth pulleys.

I am getting 8000mm/min or a bit over 300 in/min. I had the Z column laying on the table to provide a bit of moving mass.

I tried 9000mm/min but was getting intermittent stalls.

I still need to do a lot more testing, but its looking like I might stick with the Gecko G540 and the 387 oz.in motors.

Cheers,

Peter

I managed to start the Z-axis conversion over the weekend.
The new nut holder is to be made in two parts. This is so that it can be assembled into the column. The larger size of the RM2005 ballnut in comparison to the original nut makes it impractical to make the nut holder in piece.

The images below shows the original nut holder and the new one

---

The larger part of the nut holder is a 50mm cube. I now need to drill the bolt pattern for the Z-nut and drill a clearance hole for the 20mm ballscrew.

The small piece of the nut holder has the boss turned and tapped (M8) to attach to the Z-Slide.

The two parts of the Z-Nut holder will be bolted together with two M6 bolts.

I still need to remove 3mm from the bottom of the smaller piece to get the total length of the new nut holder correct.

I'm thinking about removing this 3mm by turning a boss (20mm dia) that will then fit into a matching hole in the larger part of the nut holder.

This will provide a positive locking fit rather than the two M6 bolts holing the weight of the head.

I'm not sure if a boss is required so any input is greatly appreciated.

Cheers,

Peter.

Grant and his apprentice have kindly offered to build me a new Mill stand, and it is coming along nicely.

The basic plan is depicted in the attached drawing. The stand will have 4 locking rotating casters along with adjustable feet. The idea is that the feet will lift the stand off the casters once manoeuvred into place. I got this idea from my Yamaha Pick and place machine.

The casters and adjustable feet have turned up.

The casters I were from here
TE21TPB_HB GREY RUBBER CASTORS - Castors2Go

The Feet were from here.
legs adjustable nylon stainless steel foot feet disc

The ones I chose have a 90mm base, with a M16 thread and 160mm long.

I forgot to add the picture of the stand progress. The stand is made out of mild steel 50mmx50mm with a 4mm wall thickness.

Cheers,

Peter.