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

Hi here is a good example of 4axes work.The rough is xyz then flip 180. The second part is where the 4 axes are working ''simultaniously '' .Indexer work and 4axe work are different. With the right software you will be able to do both with .
Normand
http://www.dailymotion.com/video/x9w...nc-4-axes_tech

In that video, with all 4 axes running simultaneously, notice that the cutting bit is always perpendicular (90 degrees) to the surface of the work. That was a strategy decision by the programmer. I wonder why he decided not to use the side of the bit . . .

He waisted lot of time machining the mass instead of contouring the wood last. Machining 4 axes allow also to do undercut.

Gerald,
Most likely, if he was using a package like Rhino 4th Axis, cut3d, etc...it's easier to write out a 4 face cut file with indexer being either manually written to index 4 times or as I like to do it, write four files and have Mach play them in sequence.

It looks like the file did the following:
4 - face, spiral roughing, parallel to face with collision detection for bit
1 - 4th axis continuous rotation final pass with a very high overstep for resolution.

On the larger index models, I found that the 3d model software would crash after about 3 million polygon faces. Thus, I had to do each face separate to generate a toolpath before trying to let the software "remove" all that material for a final toolpath. Computer crashes are my driving factor when trying to produce a part file.

Have a great day.
Sean

Completing the rotary axis homing system
 

A piece of copper was cut and filed to make a bump for the rotary axis homing system. A strip of sand paper was fixed on the rim of the plate and the copper piece manually rubbed against its perimeter to get the exact diameter of the rim.
It was then fixed with Loctite. I usually cover parts that I fix with Loctite with adhesive tapes, so that they are isolated from the air and speeding up their curing.
Attachment 8345

After curing, the top surface is manually finished with grit 600 sandpaper. Next the microswitch is adjusted against this bump to have the least movement.
Attachment 8346

Attachment 8347

Setting up the 4th axis in Mach
 

Is discussed in post #116 in the following thread:
http://www.mechmate.com/forums/showt...?t=2189&page=4

Did you get your 4th axis working?

Hi Brad,

Yes it is working fine and quite precise.

Excellent. I'm thinking of doing a 4th axis build like yours. I've just picked up a 100:1 harmonic drive. Im a little concerned the 100:1 isnt divisable of 360 so not sure how mach3 will go with the steps.

http://i76.photobucket.com/albums/j7...d/DSC01112.jpg

Brad.

Hi Brad, don't know how the harmonic drive will interface with Mach 3 on the indexer.
I have a 130 tooth module -1 gear fitted to my lathe shaft.
The Stepper motor has a 24 tooth pinion fitted.
Mach-3 has a function to calibrate the movement.
All I did was to set the indexer with a spirit level.
Tell Mach-3 to go 360....full revolution.
Eyeball the spirit level after this movement and told Mach that it moved 280 for instance (depending on where it stopped)
Within 3 or 4 calibrations I was going exactly one revolution when mach moved 360.

Excellent.. I'll try that method. I was doing the maths method and 1 degree movment was calculated at 555.555555556 steps per degree. I'll give the calibration a try and if it doesnt work perhaps use a pulley on the stepper 20:18 HD to reduce the ratio down to 90:1 to give an even 500 steps.

Brad.

Brad,
Maybe you would give a second thought to that. A harmonic drive is virtually a zero backlash gearbox. Interfacing it with another set of gears might introduce some backlash.
You can add as many decimal places as Mach accepts. It will not round it up. And don't worry about 555.555555 and 555.55555. it will be less than 1xE-6%.

there is a note that should be considered when using microsteps with the fourth axis. As long as the fourth axis is rotating, it will provide a fine machining, but if your toolpath should require that the fourth axis to stop, while e.g. the Y and Z axes is working on the workpiece (like making fine splines along the length of a cylinder, then microstepping will be neglected and the fourth axis will stop at full step, or at the best at half steps, depending on your wiring, since positioning will not obey microsteps (or at least this the case with my driver).

Hi Nader,

So good to hear from you. I think of you and your build from time to time and wonder how you are doing. Perhaps you would consider "showing" us your final (latest) machine and some of your results.

I'm especially interested in your indexer experience, since I'm planning to use a similar design on my next MechMate.

Regards,
John Higgins

Nader - I would also need some more inspiration! do post some pics

Brad get a servo for your harmonic drive - there are lots on ebay - they top upto 3K rpm and would definitely work with the harmonic drive

Hi John and Irfan,

Thanks. Right now I am working on another new design which is intended for cutting mainly Aluminum. Also I am doing some research and experiments to introduce a 4th and 5th axis on this machine. But I will send some of the workpieces made before.