Thread: Table traverse for Chinese mill.

Hi Guys,

I've done some more work on this design. Having decided that the tumbler gears were the right way to go. (Thanks Stuart) I remembered where I had actually seen "Tumbler Gears" in use. Right under my nose. See Picture of my Myford Lathe gears.

I had some plastic bar that was about the right size to support the pair of gears that I wanted to use. So I cut off a slice and knocked a 1" hole in it on the lathe. It was at this point that I realised that the wiper motor gearbox case didn't have a parallel sided shaft support. so after some thought and careful positioning I set the motor up on the rotary table on the mill. Actually I cheated because I couldn't find a consistent point to measure from on the outer case so I grabbed the motor spindle in the drill chuck. First I set the rotary table dead centre under the mill spindle and then locked the X and Y axis. Taking the wiper motor spindle in the drill chuck I lowered it down and carefully shimmed it up the gearbox and clamped it to the rotary table.

Hi Guys,

Don't know what happened but half my last post has disappeared !!!!

I see some effort is being made to avoid running windscreen motors in reverse.
Is it possibly worth looking for some that don't care which way they run?
Mine doesn't. In fact mine has a backlash adjustment screw in the end of the gear housing pushing on the end of the worm spindle with a little ball bearing between centre holes.
The motor end also runs against a ball bearing in the motor housing end shield. No chatter there.
I've seen an adjustment screw on several models wiper motors - maybe that's all we need to look for?

Originally Posted by jhovel

I see some effort is being made to avoid running windscreen motors in reverse.
Is it possibly worth looking for some that don't care which way they run?
Mine doesn't. In fact mine has a backlash adjustment screw in the end of the gear housing pushing on the end of the worm spindle with a little ball bearing between centre holes.
The motor end also runs against a ball bearing in the motor housing end shield. No chatter there.
I've seen an adjustment screw on several models wiper motors - maybe that's all we need to look for?

Hi Joe,

I have had mine completely stripped down and there is a steel ball in the worm end of the motor spindle but the other end is simply a plain bronze bush. There is a thin brass washer at that end though. At the end where the worm ball is there is a pressed in steel cup that the ball bears against. If you twist the shaft you can feel a tiny amount of play.

I've not seen any that are adjustable though.

Further info: The motor on mine is a permanent magnet type brush motor. It has three brushes bearing on the commutator. Two pair are directly opposite each other and the other one is set off by 35 degrees. This is probably for the low speed and the other for high speed.

Hi Joe, An adjustable ball on the gearbox end of the worm would work for 1 direction but to work in both directions it would need something to take the thrust on the other end of the spindle. I would think that all wiper motors would only normally run in 1 direction so I doubt that thrust on the other end is considered. I guess that window & power tailgate motors would be designed to operate both ways, however only designed for very short duty cycles & would not last running continuously. I used a windscreen motor on my mill table for a couple of years with no problems but the arrangement was one I copied from the net & it was set up to slide the motor a few mm to disengage the worm from the worm wheel (first switching off the motor before engaging) one day had a seniors moment & engaged drive with the motor running, that ended that set up. I like the idea of tumbler gears & also different motor for fast traverse. With the projects in the pipeline it may well be a 2015 project.
Cheers,
ian

Hi Guys,

I don't know what happened to the other half of my post and the last picture, but...

I carried on to say that I had cut and bored out the end of the gear seen on the motor shaft before I realised about the tapered casting. The bore is 8 mm diameter and I turned a taper in it to match the cone's spline on the shaft. However it bulged slightly when tightening the M8 nut. I decided not to try and remove it because it was so tight that I was afraid of pulling the shaft out of the worm wheel. The bulge makes very little difference to the gears meshing properly.
Gears-a1.JPG Gears-a2.JPG
Having successfully machined the gearbox casting, I obtained a piece of brass and turned a sleeve to be a press fit on the newly machined casting. The brass sleeve is 28 mm outside diameter and has a 3 mm wall thickness. I put a 3 mm wide flange around the bottom end so that the tumbler gears support ring would sit on it and not migrate down onto the casting body.
Unfortunately I didn't take any photographs of making the brass sleeve.

Support_Bush.JPG Support_Bush-02.JPG Nut&Snap_ring.JPG

I also turned a groove for the circlip (I think you call them "Snap Rings") to retain the tumbler gears support collar.


Support_Ring-02.JPG Support_Ring-03.JPG

This is the support for the tumbler gears. As you can see I turned snap ring grooves into them to retain the gears. The gears have a 6 mm bore and these two shafts are actually the pins that supported the original gear. Since I cut the gear into two I did the same with the original pin. Since this pin was riveted into the gearbox plate that it came out of and didn't have a dimple in the end to get a drill onto, I used a length of plastic tube slipped over the pin so I didn't damage it, and then levered it over to one side. It popped out quite easily with surprisingly little force.

Gear-03.jpg Gear-04.jpg Gear-05.jpg

That's it for now, more later.

Looking good BaronJ!

Originally Posted by BaronJ

I also turned a groove for the circlip (I think you call them "Snap Rings") to retain the tumbler gears support collar.

Downunder, we call them circlips too

Hi Guys,

Since I've done a fair bit of work on this project I thought I would catch up with some drawings of the various bits and pieces.

Mill_Table_drive-07.jpg
This one is for the brass bush that has been pressed into the wiper motor gearbox casting. The measurements are all in millimetres and are taken from the actual bush that I made.

Mill_Table_drive-end.jpg
I took measurements from the mill table end plate after I had removed it from the table. It was held on by two M6 hex socket cap screws and used two extractable dowel pins to ensure accurate location on the table end. It was quite hard to get the dowels out. They were threaded M4. I ended up using a hollow spacer, washer and an M4 hex socket cap screw to extract them. Even then I had to use a soft mallet to break the joint between the parts. There was some hard brown stuff between them and I do wonder if it was some kind of adhesive. Anyway there was a thrust race in the cavity and a 4 mm key in the key-way

Mill_Table_End-001.JPG Mill_Table_End-01.jpg Mill_Table_End-02.jpg Mill_Table_End-03.jpg Mill_Table_End-04.jpg.


Now back to the tumbler gears support ring.

Gear-06.jpg Gear-07.jpg Gear-08.jpg

These photographs were taken during a test fitting of the parts onto the motor. As was pointed out the gears all have to mesh in such a way that the drive goes from the spindle gear on the driving shaft, then to one of the tumbler gears, and then to the other tumbler gear. The third gear (the right hand one in the first picture) is offset by twice the tooth depth whilst being fully meshed with its mate on the left. I did run the motor at this point and it drove the gear chain smoothly without any binding. The 6 mm diameter pins were simply pressed into place into holes drilled with a 6 mm drill bit. Note that drilled holes in plastic always end up a fraction smaller in diameter, so the pins were a very good fit.

More later

Baron, I can't see how the gears pivot for the reverse (my excuse is that I haven't got Stuart's super human powers of observation). What's the plan?

Michael

Hi Baron,
I would have thought that the tumblers shouldn't mesh in your arrangement.
I am assuming the nylon (?) rotates around the bronze bush for reversing.
Nope, ignore that I think I may have figured it out

Phil

Originally Posted by Michael G

Baron, I can't see how the gears pivot for the reverse (my excuse is that I haven't got Stuart's super human powers of observation). What's the plan?

Michael

Hi Michael,

If you look at this picture,

Gear-06.jpg

The drive comes from the gear on the shaft in the centre. If you imagine that this gear

Driven_Gear-01.JPG

Is positioned so that it can be driven by either tumbler gear simply by rotating the support collar on the wiper motor gearbox casting. The original drawing as was pointed out the three gears were meshed with each other when they should have been arranged like this

Mill_Table_drive-04b.jpg
If you place the big gear so that its spindle is in line with the drive gear spindle and rotate the layout drawing so that one or the other tumbler gear drives it. Move the tumbler gears the other way and the other gear will drive the big gear, but in the other direction.

Does that explanation help.

Originally Posted by Steamwhisperer

Hi Baron,
I would have thought that the tumblers shouldn't mesh in your arrangement.
I am assuming the nylon (?) rotates around the bronze bush for reversing.
Nope, ignore that I think I may have figured it out

Phil

Hi Phil,

Your post just got there before mine.
I hope my explanation came across OK

Hi Michael,

Try this drawing. Move the red circled support collar by rotating either way, so that one or other of the tumbler gears is in line.

Gear-0.jpg

Got it now. I was expecting the changing of gear direction to be done on the grey plastic collar so was wondering why something was not eccentrically mounted.

Michael

Originally Posted by Michael G

Got it now. I was expecting the changing of gear direction to be done on the grey plastic collar so was wondering why something was not eccentrically mounted.

Michael

Hi Michael,

I had to think hard about it at first ! It took a while before I realised that my Myford lathe used tumbler gears to change the lead screw direction. After that it was no problem getting my head around how I should do it to get a neutral position and backwards / forwards movement. I think that the thing that throws you initially is realising that three gears are permanently in mesh whilst the large gear isn't.

Myford_Gear.jpg