Lathe Mods

You can scrap that question, Stick the first pistons other side on an air line!

The spring could be inside the hydaulic cylinder between the housing and the piston.

Yould have a manual lever allowing you to apply the desired pressure by hand, as in a woodworking lathe.

May need to brush up on the old insert image button!

I don't say your setup wont work but I must have grown up on the other side of the street.

When I see a problem like that my first thought is steppers (or servos),

The advantage of using steppers (CNC lathe) is that

- one only has to do a drawing of the shape (no need to machine a master).

- The master cannot wear out or get lost,

- It is even possible to only enter a formula for the shape.

I never really experimented with stepper motors, most of my experience was with units that drove off cam shafts and dogs, Then doing small batch work on CNC machining centers! Can you point me in a good direction, eg. stepper motor on the lead screw of the cross slide, Can´t quite figure out how to get the profile off a drawing though!

Are you trying to cut a shape that was hand drawn and therefore difficult to describe geometrically? This can be scanned into a cad/cam system such as Mastercam and converted to nurb splines or points and then easily programmed. This is something I do often. Contact me if I could help in this way.

If you have a scale representation of the contour, there is another way. Lay out a series of points along the contour which you can measure. This is a method I used to use to program contours for aerospace casting for which the contour was provided on a mylar sheet but not dimensioned. Mathematically determine an arc that passes between the first 3 points. Program an arc from the first to the second point. Do the same for the second to the forth points and so on until you have programmed the entire contour. It may sound like a lot of work, but it is faster than building a tracer lathe.

I am just curious. Wouldn't it be much easier to just get an engine lathe with a tracer attachment? That wheel was invented long ago. However if you are determined, try visiting a dealer that sells old machinery. They are bound to have mills and maybe lathes with tracing capabilities. You could have a look at the hycraulic systems that operate such machines and see first hand how it has been done for a long time. I used to set up and operate tracer mills and there are some tricks to getting them to perform accurately. They are not very fast either. You have to compensate for the tendency of the stylus to plough going up hill and leap past the contour going downhill. In 1981 I was told by fellow moldmakers that it would take too long program a CNC mill to cut 3D contours. My very first CNC project changed their minds when I did a job in less than 3 hours that would have taken a week to complete using a tracer mill. I find it hard to believe that your project could not be done much faster and easier on a CNC lathe.

I would not try to do what you want and this for some reasons: - years ago i even designed a hydraulic "follower" system for a lathe. Your idea is straight forward but considers the fluid as incompressible which is TOTALY wrong. - considering the forces on the cutting edge of the tool on one side and the influence of radial forces on the "model" the systems were ALL designed as servo-hydraulic systems with a, usually, one edge control. This allows a low force on the "model" and a high stiffness at the tool. - considering the difficulties to make such a system work properly i would suggest you use an electronic approach either step motors or brushless motors with a stroke transducer to follow the model and give the signal for the tool position control. It will be easier for you to find the helping hands to make the system stable than to find people able to master a hydraulic system without electronic control. It is a "forgotten" technology.

I like all the ideas you have given me, but I still have no idea how to control the servo motors! I have a spare laptop with lots of ports free, I have a lathe, I can get servo motors, question is how to use one to control the other! my computer programming skills are Sinclair ZX81 standard with no connection to the outside world! If I put a servo on the cross slide and one on the lead screw of the saddle, I can see the fundamentals of a CNC but the servos need control and that is the part that foxes me!

If anybody can guide me to a fundamentals programming website or offer advice about this, it would open up a whole new world to me! I may even put a servo on the milling attachment!! (maybe pushing my luck on that though!)

I would recommend the stepper motor approach. The main reason for using stepper motors is that you don't need any feedback system to know where the motor is. Provided you know where the stepper motor is at start up it just a matter of keeping track of how many steps and in which direction you have gone to know where the motor and whatever it is driving is.

You can purchase stepper motor control systems like this one that run off the parallel port of a computer and I am certain that if you look there are ones that run off a USB port.

Another alternative is to use something like a PIC microcontroller kit to build you own stepper motor controller. There is a PIC microcontroller kit that comes with all the circuitry and a small stepper motor that only requires you to write the program to get you going.

I don't know how much you know about stepper motors, but, if you are completely in the dark would you like me to write up a short overview of how they work?

Yes please, I am completely in the dark! my plan now is to go with the stepper motor idea. to me it seems more sensible and more versatile! but, I am in the dark as to how to set it all up! If I can get this working, I could do my telescope as well!

thanks for your help Masu and everybody else. T.B

To understand the stepper principle you have to look at a pen plotter.

If you imagine the x axis along and the y axis across the job.

Plotters are usually controlled by a graphical command language like HPGL or gcode.

Example PA 100,10 ; Plot absolute , PR x,y plot relative :

The steppers are fitted in the place or additional to the handwheels.

Steppers can be controlled with a plotter, A stepper driver (Gecko for example) or a proper control card (visit Galil).

I am for cheap DIY solutions and it is really easy to convert an old machine into CNC at a fraction of the price.

Now that idea is a corker! The motors are strong enough to do this?

The input was till now of qualitative aspects, the question M. Truman Brain asks for a quantitative answer. Is anybody able to give him a possibility to estimate the cutting forces and the different motor torques he will need? I have not such formula but one of the gurus mast have either a site or in a book the necessary relationships.

As far as i know cutting forces depend on the yield of the material, the cutting edge geometry, the position of the tool and the cutting area. But i have not coefficient values. If we do not supply this information he will not be able to make the right choice and his investment will be a loss.

Normally you get 3 forces specified by the equations:

one in feed direction

one in tangential and one in radial direction.

The second and third generate frictions in the guide you must take into consideration and the one in axial direction gives the main resistance to forward move. The motor torque (is specified) MUST be higher the resistance torque if not you can loose steps and the position is no more directly related to the number of send pulses. The ratio should be at least 2 since there are also masses to accelerate.

You can adapt your motor and resistance via changes in the cutting area

= depth x feed/rev.

Hope it will help.

If you do not get an answer i shall try to find something to help you but since i am not a manufacturing specialist such informations are not usual for me.

Sorry about being slow at responding but I got tied up with my blog and it tool much longer than I anticipated.

A stepper motor is a motor that has multiple coils wound as part of the stator and a rotor that is made up of a permanent magnet with multiple north and south poles. The whole thing is arranged so that if you energize each of the coils in sequence the motor will suddenly jump from the current position to the next around the stator.

Now that sounds confusing so lets look at a 4 phase motor that has a 6° step. The coils will be numbered some way that gives you an order so lets say they are labeled A, B, C and D.

To drive the motor forward you disconnect the power to the coil that is has power on it and energize the next coil in sequence. So, if coil A had power to it and you then removed the power from A and applied it to B the motor would step forward one step or 6°. If you then removed the power from B and applied it to C the motor would mover forwards a further 6°. So every time you move forward from one coil to the next in sequence the motor will rotate through 6° and then stop in that position. The other important thing about stepper motors is that they will not burn out if the rotor is locked, quiet the contrary they are specifically designed to be able to remain at a fixed position with power applied to one of the coils. So if you energize each of the coils in sequential order A-B-C-D-A-B and so on the motor will rotate through 6° with each step from one coil to the next.

If you energize the coils in reverse order A-D-C-B-A-D-C etcetera then the motor will rotate in reverse through 6° with each step from one coil to the next.

The beauty about stepper motors is that if you know where they area at startup and keep track of how many steps you have stepped them through then you know exactly where the motor is without the need for any other feedback circuitry.

Now the type of motor I have described is one that you more than likely seen. If you have a quartz watch that has an analogue rather than a digital display then the motor that drives the hands is a 6° stepper motor. Each time they step from one coil to the next the second hand advances by 6° which happens to correspond with how far apart the second marks are on the face of your watch.

As I mentioned earlier they are designed to be able to operate with a licked rotor. If you try and rotate a stepper motor that has none of the coils energized you will find that while you can rotate it relatively easily it will only stop in defined positions. If you tried to rotate the motor while one of the coils were energized you would find that it was very difficult to turn. That is because you are trying to fight against the motor and to get it to move This is a huge advantage when you are trying to position something that may try and force the motor to rotate in the opposite direction.

Now I have described a 4 phase 6° stepper motor but you can get stepper motors that have different numbers of coils and are designed to step through different angles. You will need to figure out how much the motor steps yourself but it isn't that difficult, just make sure that each step results in less than the minimum resolution of the position system.

So, in summary, a stepper motor is more a motor that you can specifically tell where to move to rather than a motor that can rotate and in a control environment if you keep track of the number of steps you have made the motor move through then you know where the motor is in relation to it's start point. By stepping through the individual coils in the forward sequence the motor will rotate forwards through a defined number of degrees and by reversing the sequence the direction of rotation will be reversed. While any of the coils are energized the motor will resist being rotated by external forces and can tolerate sitting in one position with the power on indefinitely.

The other neat thing is you don't need to worry about controlling the current to the coils, all you need to do is supply them with the appropriate voltage so the circuitry is very simple and ideally suited to controlling from something like a microcontroller.

Hopefully that will give you an overview of what is possible with a stepper motor and why they are really hard to beat for positioning control systems. Here is a link to the Wikipedia article on stepper motors that you may find helpful.

Thanks Masu for your response, While I knew about some aspects of the stepper motor, I didn´t realize there was such a large variety! I need to think about the cutting forces and such to be able to find the right ones! As most of the work I will be doing is one off or very small batch, the initial roughing out will be done by hand and then finish the profile with the computer! ( or if I can do all by computer if I feel inclined) I think the biggest depth of cut I will be making is about 3mm at a relatively slow feed, maybe 0.1mm/rev! I´m not really interested in cycle times , so I´m not looking to optimize my speeds and feeds! My main worry now is controlling the thing! the plotter method seems quite good but need to be able to control the feed! The plotter uses a pen with no problem on the speed of the traverse. this is what I need to control if I go for this approach.

I have no knowledge whatsoever on connecting the servos to the computer or programing the computer! (oh my god I hear you cry!!) Programming CNC mills and lathes is something I can do but that is using Fanucs programming language! I have looked up a few sites but they don´t really explain what goes where and why!

I promise that if I get it running, I will put some finished pieces on display for all to see! Any more help will be greatly appreciated! Thanks

Steppers

I have used a few HP 9872 A3 plotters to drive some CNC conversions. The steppers were over designed and should be strong enough for a small lathe. The plotters were available in the late 70's. They used a HPIB (GPIB - IEEE488 predecessor) interface.

Most of the conversions are still in everyday use.

Lately Some of the electronics (caps etc ) started to fail and repairing them becomes a bigger challenge. The interfacing with modern fast cards and computers also gives problems.

The latest conversion was done using the steppers from the plotter but drive them with a Gecko driver.

There are some new steppers available with the controller build in. Control could therefore be obtained from 2 signals (+ ground) from the printer port. (step + direction)

To drive the steppers printing :

1) A for positive and C for negative step .

2) D for positive and F for negative step on the second stepper

Or a bitwise combinations of the 2

I use Borland Pascal (BP7) in real mode running Windows 9x in DOS mode. (Least interference)

Using direct access to the printer port.

Real fast and accurate motion can be obtained.

It can also work under XP if you strip out most of the MS baggage.

Shop around and see what you can get – check the torque available and required - feel free to post a new question or send me a mail.

This stepper motor kit would probably be the way to go. Basically it's a microprocessor that has all the circuitry needed to dive the small stepper motor it comes with. It connects to the parallel port of your PC and comes with all the software you need to drive it.

This link will download the kit manual and software.

Playing with this kit will give you a good understanding of how stepper motors work and how to drive them from a PC.

Once you have an understanding of how they work you can use that knowledge to design and select the final stepper motors for your application. You should be able to reuse the circuitry from the kit to drive larger motors with the addition of a handful of power transistors.

This book Stepper Motors and their Driver Circuits may also be a good investment.

I just found this site Building Inexpensive CNC Machines that may be of help. I have only given it a cursory look but it appears to have a whole stack of information that is relevant to you application.

If you get stuck selecting the correct stepper motor drop me an email and I will go through what information is required and work through selecting the appropriate stepper motor for your application.

I just found these links that you may find helpful:

1. USB Stepper Motor Controller: This discusses the use of a small controller board that they manufacture to control three stepper motors giving you three axis control.
2. Standa Microstep driver with USB Interface: This is a 1 to 4 axis stepper motor driver that comes with software and connects to the USB port on a PC.
3. Controlling Stepper Motors through Parallel Port: Electronic Schematics for Hobbyists article on designing, building and driving stepper motors.
4. Home Made CNC Machine: Hacked Gadgets: This will take you to the Hacked Gadgets Forum where numerous people show what they have built.
5. Mecatronics Demonstration Kit: Microchip This is a kit that is manufactured by Microchip and comes with both a stepper motor and brushed DC motor that you can use to learn servo control using microcontrollers. While it costs US$149.⁹⁹ it comes with everything you need including software and USB interface that you need to design your final circuit. Once you have developed you circuit you can then use it to program the microcontrollers you use in the final design.

Unfortunately I couldn't find much on building a USB stepper motor controller. This is probably due to the complexities of the USB system. USB is a great idea and makes a lot of sense but it's not like the old serial or parallel ports where you can plug things directly into a computer. There is a very complex protocol that covers how things connected to a USB port actually communicate with both the hardware and software within the computer. If you wish to go down the path of using a USB port then I would suggest purchasing a USB Stepper Motor controller. There are plenty of them out there that can be purchased off the shelf starting at around US$100.⁰⁰ for a three axis controller. There are plenty of people manufacturing either PCB or complete units that come with all the software and all you need to do is add the appropriate stepper motors. Do a search on the net for

usb AND "stepper motor" AND controller OR driver

You can then select the most suitable unit and supplier. Microchip are a reputable company that supply you with just about anything you would ever wish for in the kits including software, manuals, tutorials and links to download a hole host of goodies. They also deliver thing in time frames that most companies can only dream of. I purchased a PICkit2 from them about 6 months ago and it arrived at the front door less than 48 hours later. Considering I live in Sydney, Australia and it takes about 16 hours in a jet to get here from the USA that's extraordinary. I also purchased some equipment locally at the same time which took over 3 weeks to arrive and when it did arrive it wasn't what I ordered.

Thanks ever so much Masu, this is just what the doctor ordered! I will have a look over all these sites. I know what you mean when you say "I ordered it 3 weeks ago, and its still not here!" I ordered my lathe 2 months ago from England and it´s still not here, last time I rang them they said it was on the back of a lorry somewhere in Spain! A couple of weeks ago I ordered some telescope lenses from America, I followed the progress on the net and to my surprise, the log changed from "In transit" to "arrived at destination". At that second, there was a knock at my door and there they were! It took under 2 days! So thanks again, and I will let you know how I get on, Cheers Masu et al once again.

Ok le me take a stab at it.

Take a rod of whatever length necessary to encompass the 2 parts.

Attach it at both ends and at the center so it pivots. What you are turning will determine the thickness needed on the rod. The rod will also need a milled flat on it.

You then can make a couple of short arms that can lock to the rod at the pivot point. this will have to be don in such a way to prevent movement or flexing. These arms will hold the tooling. The final tip placement wil have to be set to arc into the centerpoint of the lathe

I have done this on a wood lathe but not metal so don't know if you cold make it work for cutting hard steels but light metals I think migh work.

It all depend on the load being placed on the pivoting arms and size and depth of the cuts.

Just a thought....maybe should keep em to myself.

My thoughts exactly Double j b, except I have seen it done with the 2 mill points connected to a single plate (resembling one side of a door hinge) that slide back and forth on a fixed hinge rod. No secured center point necessary it the rod is stout enough.

I have done this before with simple inexpesive lathes. I mounted all of the xyz in relation to each other I changed the compounds/tool holders to linear bearing tables and connected them to each other with heavy tie rods. The tool posts and tools were the insert type and once it is set up it was a pian in the ass to try and use it. I finally said "screw it" and put my money in a used computer controlled lathe and the software to run it. This did a very good and fast job of superior repeatability and cahgeing to a different part was very simple. The cheap way if linking lathes makes a big scrap pile of your stock material. It doesn't matter if you use hydraulics your results wont be better. Your hydraulic pantograph will allways give you cause for heartache. Any air or gas will screw it up badly any seal leakage will be frightful and irretreivable. A panto will work for baseball bats and chair legs ect, and you will need them to be progressive you start with something big and use several panto patterns until you get to the finished size. If you are machining metal it is not prccticle.

Clearly there are two methods being suggested here...you could purchase a very expensive CNC lathe to churn out part after part, and all you would need is to pay some minimum wage kid to put the new pieces in and take the finished piece out, and stand idly by why the lathe makes the chips. Or you could pay a highly skilled craftman to make each piece individually...bet thats what you are doing now and thats why you want to the copier function.

Or for less than a hundred bucks you could build a little carriage to hold your chisel at the right angle. this little carriage sits flat on the same table the lathe bed is sitting on and you can push it easily around side to side. You have to hold it flat, but when you push it into the spinning workpiece, it cuts into the wood. It will cut into the wood until the base is stopped by the profile you have jigsawed out of hardboard (or thick brass, or whatever) and mounted onto the lathe bed with a few wood screws. You can change the profile any time you want in only a minute or so.

Then, your minimum wage employee, instead of hanging around watching the cnc machine make chips is actually guiding the tool, and making chips himself. Building skills, self confidence, and ability.

You can buy these little copier carriages, but I made my own from a chunk of 6 by 6 by 6, and lathed out the spindles for my staircase in about 6 per hour, including sanding staining and waxing. (processes which are all done without even stopping the lathe)

I think it was Springfield Armouries which invented the original copier lathe...which wasn't really a lathe per se, but rather a dozen router heads mounted on a solid frame, each cutting their own gun stock. A skilled worker could guide this massive machine and produce more gun stocks than anybody else, and so they got the government contract.

The above is for a wood lathe of course.

Not sure how you would do it with a metal lathe.

My Aime is to turn and mill fancy bits out of stainless and aluminium to decorate and enhance the look and feel of custom chops! My funds are small and here in SE Spain, you can find anything you want as long as it has something to do with tomatoes!! Sorry but no local 2nd hand machine shops of any kind unless it has something to do with tomatoes! I can get servo motors because they use them on there tomato machines and lucky for me...there is a st/st & Al supplier near but only the sizes of bar and plate that they use on the tomato machines!! so there you have it in a nut shell! I´m not too keen on tomatoes either but that´s another story! I´m going to aime for the servos, so if I can get feedback on that, it would be great! Cheers guys.

I remember my grandfather, he was a carpenter, In his loft were all kinds of old woodwork tools that he had made and remade, He had a beautiful wood-turning lathe that I loved to use, What a great smell carpentry has! Later I started in a factory with metal and loved the mechanisms, now I just enjoy the creativity of it all! Long live creativity. Anyway, if you could help me with the stepper motor problem it would be great!