The overall concept of the MM's Rack and Pinion design - springloading & antibacklash

[Gerald_D]

These drawings show the assemblies:
M5 10 100 A
M5 10 200 A

http://www.mechmate.com/Forum/messages/12/1929.jpg

The motor (or motor & gearbox)is screwed to the Motor Plate M5 10 012 D which is hinged to the car. The spring holds the pressure of the pinion gear against the rack. The stabiliser screw rides in a slot - it allows the motor plate to swing but not "flap" around. Teflon washers are fitted where the motor plate slides against the car.

[plain ol Bill]

Well after having to go out of town to work for a long period and then my shop largely disappearing (kids "borrowing" tools) during the absence I am again looking at MechMate. I have been looking thru the drawings again and I KNOW there is a specific dwg. in there somewhere showing the mounting of the racks. After going thru them 3 times I'll just ask: Which dwg. number shows how the racks are mounted?

[sailfl]

Bill,

Look at 10 20 200 AA. I hope that helps you.

3M Tape 4955.

[plain ol Bill]

That's the one. I must have blown by that at least 10 times w/o seeing it. Oh well - I never claimed to be smart. Thanks for the reply.

[sailfl]

Bill,

Don't beat your self up. There are a lot of drawings and a lot of details. I think every one has had the problem of not being able to find a detail they need.

[Mongkol]

Ton started the thread before the posts above were copied into it . . . .

Dear All,:)
I am finding the concept of Rack and Pinion design. I am building plasma table at 4' x 8' ft. Who can advise me for the picture of rack and pinion design on X-axis and Y-axis.? I don't still understand of the method of design of each axis.
If who has the picture also,I would like to big thanks.


Best Regards,
Ton
mongkolnum@gmail.com

[domino11]

Ton,
If you go to the download section, you will find links to download the Mechmate plans which detail the rack and pinion design that is the Mechmate.

See here.

http://www.mechmate.com/forums/showthread.php?t=376

[Mongkol]

Heath,
Thanks for your help. I downloaded Mechmate plan to find the concept of rack and pinion design. I am still puzzled with the connection and holding of motor with rack.( of each axis). It's difficult to imagine from the 2D drawing.
I don't know this drawing was written from solidwork or not. If yes, I want to download 3D it. Is it possible?

Ton

[Gerald D]

All 4 axes use a similar method. The motor swings against the rack and is held by spring force to eliminate backlash. See some build pictures:

http://www.mechmate.com/forums/showthread.php?p=4209&postcount=81

http://www.mechmate.com/forums/showthread.php?p=7257&postcount=114

http://www.mechmate.com/forums/showthread.php?p=8392&postcount=86

It is simpler than what it looks!

[Mongkol]

Gerald and All,
Big Thanks for information!!. It sound like the Y-axis use 2 stepping motors ( left and right)to control. Is this correct?

Ton

[domino11]

Ton,
Usually the X axis is the longer of the two. This one has the two stepper motors and the Y axis (usually the shorter of the two and the one the Router Car runs on only has one Stepper motor and one passive hold down bearing assembly.

[Mongkol]

:)Big Thanks for detail

[Mongkol]

Gerald and The Experter,
From your design,I am little puzzled with X-axis. Is it necessary to have the two stepper motors? It's possible or not if I only use the one stepper motor with double high torques.

Ton

[Alan_c]

Using only one stepper on one side will NOT work. I demonstrated that to myself while I was setting up my machine, one x-motor at a time, the other end (without the motor engaged in the rack) of the gantry swings quite dramatically when jogged, it lags behind on start up and overshoots on stopping. one is not able to flex the gantry like that by hand but the power of the motors is incredible - so in short its not possible.

[Mongkol]

Hi Alan,
Thanks for your comment. I found Samson machine from this website http://www.samsoncnc.com/. It only use the one motor to drive of each axis.He use the rack-pinion method as same as Gerald design. I am confused why does it work smoothly.

Mongkol

[Gerald D]

Ton, the samson machine has a very light gantry and is only use for plasma where there is zero cutting force. On the MechMate we have very high sideways cutting forces and therefore also a much heavier gantry.

[MetalHead]

When I put in my Plasma system I wondered the same thing. I wanted to have a dual purpose system. But I learned it takes a lot more power to drive the router machines because the plasma never realy touches the work so the plasma does not need to be as rigid. My Dynatorch also has one driver for x, but the cool thing they do is use a driveshaft (red rod under the gantry) that transfers across the table to the other side to keep the system square. http://www.youtube.com/watch?v=VIwZUXPJwww

I was wondering about keeping things square with two motors, but after reading a post with 2-203V on one PMDX channel for the x I figured that was a good way to help keep the motors in sync as long as you zero the machine at startup.

I decided against a combo machine becuase I have since learned fire and wood are not good partners .... :D. (Joking of course) If you have never seen plasma in action just think about where all the saw dust gets to while the router is cutting. Now imagine that is fire (kind of like a sparkler on steriods). Best to have two seprate machines. http://www.youtube.com/watch?v=QzeEoNCUsVM

[Gerald D]

. . . . keep the motors in sync as long as you zero the machine at startup. . . .

The motors' detent torque keeps them in sync while the motors are shut down. We don't normally zero the machine at startup, unless we suspect that someone has bumped it out of square.

[Mongkol]

Hi Gerald,
Thanks for your reply. I feel clear. I agree with you the router machine have to touch on material but the plasma machine don't need to touch. Then,It's necessary to have the two motors of X-axis for router machine.
I have one question.
How many torque of motor do you use for each axis?
The 400 Oz-in stepper motor for each axis is enough ? Pls advise.

Mongkol

[Gerald D]

Selecting motors for the MechMate (http://www.mechmate.com/forums/showthread.php?t=1114)

[Mongkol]

Gerald,
I will choose at third choice.

Big Thanks
Mongkol

[Mongkol]

Hi Gerald and All,
I am designing table by using mechmate method and I can not find the plate-supportmotor drawing on the downloaded file.I am little puzzled with Mechmate design and have some questions.
1) I found two holes on the plate-supportmotor in the drawing.I would like to know what is the function of two holes.
2) I know points 1,2,3 and 4 screwed to hold the motor on the plate but I don't sure the design of Fixed-A and Slotted-B.
Fixed-A, This point is fixed with screw to be rotation point or not. Is it correct?
Slotted-B,This point is slotted hole for plate-motor to move flexible or not. Is it correct?
I have not ever designed with rack-pinion method. Pls advise.

Hope your help
Ton

[Gerald D]

Point A is the rotation center.

The slot at B is an arc with the center at A

At A and B, the screws are tightened against plastic washers - the motor plate is inside the sandwich of plastic washers. The motor plate can move inside the plastic washers.

The spring rotates the motor plate counter-clockwise until the pinion gear is against the rack.

The function of the extra holes is for mounting the gear-type Oriental Motor's gearbox.

[Mongkol]

Hi Gerald,
1)I am puzzled why do you use plastic washer. Is it possible to use metal washer? Pls advise.
2)Two holes from picture,Do you mean that they are extra holes for Oriental Motor's gearbox. it's right or wrong.
Assume,If I use stepper motor from 34HS9801.I can not directly connect with pinion on motor. I should have the timing pulley to reduce the revolution of motor. Is it correct?

Ton

[Gerald D]

1.) The rack is not perfectly parallel to the rail. As the car moves along the rail & rack the pinion must move up and down a little bit. The motor slides inside the plastic for this small movement. The plastic can be tightened for a controlled friction grip. Steel will also work, but then the tightening, lubrication and corrosion are critical.

2.) Have you seen drawing M5 10 312 P? The holes are explained there. (bottom left)

[Mongkol]

1.) The rack is not perfectly parallel to the rail. As the car moves along the rail & rack the pinion must move up and down a little bit. The motor slides inside the plastic for this small movement. The plastic can be tightened for a controlled friction grip. Steel will also work, but then the tightening, lubrication and corrosion are critical.


2.) Have you seen drawing M5 10 312 P? The holes are explained there. (bottom left)

Gerald, I clear for item1 and item2 for your help.
I have some questions in drawing M5 10 312 and picture as below.:p
1)I saw the drawing M5 10 312 and found no.8 description show M10 fender washer. I would like to know the material of fender washer is teflon ( plastic) or not.
2) From the picture, I unclear the drawing of plate-supportmotor
2.1) What is the angle between y' axis and c'axis ( spring axis) ? 45 degree or not? Is it necessary to concentrate 45 degree ?
2.2) What milimeters is the distance from point A to B about ?
2.3) Fixed spring,this is an arc with the center at A or not. What milimeters is the distance from point A to fixed spring about ?

Sorry if I disturb you
Ton

[Gerald D]

1) It is steel. You can put plastic under it if you want.

2.1) y' axis has no meaning.
2.2) & 2.3) Use your CAD program to open the .dxf files - there you can measure all exactly.

Enough of those questions now.

[Mongkol]

Gerald,
Big Thank for the detail

[jvfc]

3558

3559

3560

3561

3562

[Mongkol]

Vladimir,
Big Thanks. It's easy to imagine.

Mongkol

[jkountz]

Gerald, I have a question that may be obvious but I just want to make sure. Is the spring the only thing that prevents the gantry from "riding" up or down under pressure? I know the gantry rides on the v bearings/rails but there doesnt seem to be anything to keep the entire gantry from lifting up. Does the R and P perform this function as well as drive the gantry??

Thanks!!

Jim

[bradm]

Jim, you haven't considered gravity. The gantry is non-trivial in weight, especially compared to the vertical forces of a cutter that isn't being abused.

In the cases where the spring plus the weight aren't sufficient to overcome the vertical forces, it's a very good thing to have the gantry ride up and relieve the situation. Especially if you have proxy sensors, since one of them will fire (unfire?) and hopefully cause a machine shutdown.

[smreish]

Brad,
I have frequently tried to run the machine feedrate past it's ability to cut and have been happy to see the gantry ride up and shut down the machine. When doing 40+ hours of 3d cutting in a really hard surface it's nice to know the machine is sometimes smarter than the operator trying to make it do more than it should with a dull shaper!

[Mongkol]

Dear All,
Assume, I have rack-A at length = 1500 mm and rack-B at length = 1500 mm. M=1, If I need to use the total length of rack = 3000 mm,
I would like to know how to join rack-A and rack-B at the end rack together.
Pls help advise.

Mongkol

[Gerald D]

See drawing M2 10 110 W

[rick748]

Hi All,
Just about to start my Mechmate build and on the preloaded pinion side is it only the 12Kg preload on the spring that stops the pinion trying to climb out of the rack?

[Gerald D]

The 12kg spring load gives about 20kg load at the pinion due to the leverage effect. This has been found to be enough force to prevent the pinion gear from climbing out of the rack - the motor will stall first.