Yes that would be about ten minutes per full step.

The reason I like belt reduction is because backlash can be pretty good.

Impractical for large reductions needed to handle large diameters though.

My rotary axis is based around a small worm drive right angle industrial gearbox. 40 to 1. It has about 15 minutes backlash which I compensate for in Mach3.

Again this backlash would be unworkable for large diameter work. I only do small (up to 150mm) jobs. The inherent stiffness in the gearbox helps with the backlash at these small diameters.

I think if I wanted to do large work I would look for a harmonic drive. Theoretically backlash free.

I see on a link I found here on the forum that OM has a harmonic drive model,

http://www.orientalmotor.com/product...ep-motors.html

50 to 1 and 100 to 1 ratios. They are probably very expensive.

Greg

Greg I have picked up a harmoinc drive gearbox from ebay for $100, that was like a year and a half back its a 1:100 reduction, never got a chance to use it - may be now!

I bought this gearbox to replace the Oriental Motor's.

Later I will use the oriental motor to make a unidirectional indexer to make big timing pulleys which are extremely expensive over here.

Here you can find the specifications:
http://www.vgmgear.com/DATA/PDF/VGM.pdf

Attachment 6849

Nader,
Are you planning on using the stepper part of your oriental motors? I think I remember it being posted here that the gearbox could not be removed from the stepper. Cannot remember why at the moment though.

Lots of used harmonic steppers available on ebay - take a look here
http://business.shop.ebay.com/Electr...=p3286.c0.m282

http://shop.ebay.de/?_from=R40&_trks...All-Categories

Thanks Heath,

I was going to dismantle it to see what could be done inside it. for the new gearbox I bought a new stepper motor.

I am still amazed what good is this motor for? With so much backlash.

Greg,
I asked for the price of a 30:1 harmonic gearbox. its price is astronomical down here. Equivqlent to $2200! i.e 10 times the gearbox I bought recently.

Irfan,
I think 100:1 ratio will be too slow unless you use it with a servo. I ran my 36:1 with around 750 rpm and found out the speed is frustratingly low for a lot of jobs.

Tailstock finished
 

Here are final pictures of the tailstock:
Attachment 6900

Attachment 6901

Attachment 6902

Attachment 6903

Continuous traveling distance along the Y axis.
Attachment 6904

Amount of sway for yaw adjustment.
Attachment 6905

The following picture shows the top profile of the tailstock relative to two 16 mm mdf boards. I used a 100mm diameter handwheel (which was the smallest size available). If 80 mm was available, the total unit would be clear off from the tool mounted spindle. The chuck is on the home side dead zone of the table and spindle never reaches it.
Attachment 6906

Future jobs:
Placing the homing microswitch.
Design some kind of brake for the PK motor in order to confine its free movement while machining, along with backlash definition in Mach.
Make arrangements for attaching the new gearbox to a separate stepper motor, using the existing construct.

Nice going Nader…
It’s clean…I must say, I like the way you execute & make things happen.
Congrad….Robert ;)

Thank for nice Information, it's a great concept :)
With your Picture very clear to understand, what's you want to say. Thank again.:D

Nader
I used pk296sg7.2 . May be you should power up motors to check backlash. I see backlash when no power, but while working or holding, I see no backlash or its effect on work.
I am not familiar with gear box.

Thanks everybody.

Sharma,
Thanks. You have a point. I will try this too and see how it goes.

Greeting to all and sorry for the delay.

Following the previous post agenda, here are the new progress.

1- I was thinking on this scenario for the case of the PK296A1A-sg36 motor:
How about gripping the output shaft tightly, with some polymer material, in a form that the clamping pressure on the shaft be adjustable (say, like drum type brakes on a vehicle) which will confine the shaft’s movement under normal cutting forces, but obviously less than the torque exerted by the motor and the gearbox during movement. The idea is to localize the backlash only to directional changes of the motor and assign this amount of backlash to MACH. Please comment.


2- Design for the new gearbox
New Al plates for the motor side and chuck side of the gearbox.
Attachment 7105

I use an old height gauge for marking up the parts. The blue dye is just a refill for water proof markers.
Attachment 7107

Center pinning is done under a magnifier, first with a 2.5mm sharpened ejector pin for precise location and then the ordinary center pin.
Attachment 7106

The finished parts:
Attachment 7108

A new motor is attached to the gearbox.
Attachment 7109

Attachment 7112

The new gearbox needs a new shaft and chuck plate. The procedure is the same as the previous one.
As you have noticed on the new gearbox, it has a keyway shaft. I will try to make the matching guide on the inside of a hole using a method named “Chiseling” (just google “keyway cutting” and you will find the sources). The idea is to make a hole, (in my case 4mm in diameter) and then square it with a 4x4 mm tool steel either on a lathe using the support movement, or a mill or drill press, by minute amounts of feed.

A plug is machined to the exact size of the hole, which has a pulling lug.
Attachment 7110

Attachment 7111

The drilling surface should be exactly the height of the hole, otherwise the drill will slip off its position. The shaft diameter of the gearbox is 12mm and the overall diameter and the height of the key is 13.5mm, so I have to drill 0.5 mm inside the perimeter which falls on the pin itself.
The coloured area is to provide a contrast for better viewing.
This is the setup so far. I will cut the keyway by tomorrow and will post the results.

Length
 

Nader,

Could you verify length of these parts?

Thanks,

Sharma,

I have left the drawings in the workshop but for a visual approximation consider these:
The Chuck and the hand wheel are 100mm diameter.
The screw in the tailstock is 24mm.
The bearing is UCF205, the bolt disntances in which are 70mm.
The angle iron is 120x120x10mm.

If anyone interested, I could post the drawings after completion and debugging.

2- continued…
This, I had not done before but it was an exciting experience.
The flange and shaft part was put in the freezer and the plug is heated and hammered down into the hole. This should be done, otherwise the tip of the drill acts as two teeth gear and will try to rotate the plug inside the hole. This should be done quickly or else the plug will get loose in the hole. A center drill provides a better positioning way that ordinary drills.
Attachment 7194

The guide hole drilled:
Attachment 7195

Lug pulled out. As you have noticed there is a slight draft towards outside of the plug.
Attachment 7196

The tool is a 4x4 mm HSS, ends sharpened in this configuration. Both ends will be needed to cut opposite walls and the top wall.
Attachment 7197

The working setup.
Attachment 7198

I did the job on my press drill. Tightened the pulley as much as I could in order to restrain the chuck rotation. The feed was 0.1 mm and several passes of the quill were required to scrape the metal. The total process was about 20 minutes.

The tool being about 100mm in length, flexes along the height of the hole towards the inside of the hole. After completing the initial phase, a slight inclination should be given to the part so that in the second phase the top wall becomes straight cut.


The finished job:
Attachment 7199

The cut keyway had about +0.1 mm tolerance sideways. It was satisfactorily eliminated by a 0.1 mm shim and now the assembly has no noticeable backlash.
Attachment 7200



These are my sources for shim material: Aluminum sheets inside a blown capacitor (0.1mm) and shaving blades which are cold rolled stainless steel, precisely 0.08mm thick.
Attachment 7201

The new assembly now in place, attached to the previous construct with no changes.
Attachment 7202

3- The homing microswitch
This is the preliminary setup for the microswitch assembly.
Attachment 7203

Attachment 7204


Later a simple bump will be filed and polished from a piece of brass (only for its contrast of colour) and glued to the outer rim of the chuck holder by Loctite.


So far this project is completed except for some minor refinements and adjustments which I will post as progressed.
It will remain till the machine is completed so that we could see how it will actually work.

Nader…..Love this !
Neat the way you thought out your complete 4th axis machining steps & process, with basic tools !
I like your DIY ways & approach.
Congrad, Robert ;)

Nader,
Inspiring and nice work.

Thanks Robert,
I very much hope they are useful.

Thanks Sharma,
A couple of picture showing the approximate dimensions:

Attachment 7252

Attachment 7253

Thanks Nader.

Nader. Thank You for a nice work

I have never done 4 axis machining before and all I know is theoritical or even deductive.
I assume:
On a rotating axis (in this case B axis) only Y and Z axis will be engaged. The rotating axis will be a X axis shaped into a cylinder.
There is a case though that I believe will need X,Y and Z axis movements. Suppose you want to carve a shape on four sides of a rectangular shape. Therefore the rotating axis will only do an indexing job. The rest is machining in YZ plane with incrementing X or XZ plane with incrementing Y. so X must have an offset relative to the center of the chuck (like below picture):
Attachment 7804

Now here is the trouble.
According to my proposed layout to move the B axis to the end of the MechMate, there will be very little space for X travel before hitting the limit switch. In the case of my machine it is about 70 mm, which means a rectangular shape of ony 140 mm could be worked. As you can see I have moved the spindle to the last holes of the carriage square beams. Now, the tool changing will not be clear off the table, as it was before. And the dust collector head should be mounted on the spindle side.
Attachment 7805

It would be wise to move this assembly further in, to obtain more X axis travel.

Sorry for the upside down ruler. I noticed it right know.

If you are using Mach3 as controller you might want to designate the rotary axis as A.

Yes I know by convention it is a B axis, but Mach can only visually represent an A axis rotary toolpath. Not B or C.

My rotary is set up in the same configuration as yours and strictly speaking is a B axis but I call it A for that reason.

Any 4 axis CAM that I have used allows you to designate it either way.

At least it has proper markings on it and not medieval english. :)

Greg

Why don't you want to use the x-axis to the right side of the rotating axis, or "behind" the rotating axis from where you will be standing?

Greg,
Thanks for the valuable notice. I did not know that. I have another question though. In Mach we normally use the A axis, slaved for the X axis. Should I define the B axis to be slave to the X axis, and then define the A axis as rotary?

Gerald,
Do you mean something like this arrangement? I wonder, do I have to reconfigure Mach with a new axis definition, in which Y axis has two motors and X with only one, i.e. exchanging the X and Y axes?

Attachment 7819

I was wondering why you wanted to work against the limit switch of the x axis. I suggest you consider to work on the other side:



You can configure the axes any way that you want, in any direction that you want.

Gerald,
Please take a look at the last two pictures of:
http://www.turningaround.org/4_axis_mill.htm

Suppose you want to carve a relief on each side of the cube part.The rotating axis will be fixed at each 90 degrees index and the relief will be cut in ordinary XYZ travel. Now, the maximum width (in this case the X travel) will be limited to 2 times of the distance between the center of the chuck and the ultimate distance that the X axis can go (i.e. to the end limit), in my case this width is limited to 140 mm.
This would possibly be the only case that one might need X travel. In other cases your notion is right.

Nader,

The link doesn't work for me.

Yes, Art did some redesign of his site a little while ago. Some of my old links do not work either. The site is still up though.

Thanks for the reminder. Heath is right, some pictures are omitted.

Visiting the following link:
http://www.turningaround.org/joecnc_hybrid.htm
The second and third picture from the top shows the problem I previously mentioned.

Studying his design more closely, presuaded me that this should not be worrying. The square part, as big it might be, could be done on a separate piece using XYZ ordinates and mounted to the circular section.

Thanks for the presentation, its great to see an idea come to life.

Time for me to open Solidworks and get designing