11th October 2006
Not having any experience with steppers, I decided to err on the safe side and chose 56mm frame steppers for all axis. All three steppers have been salvaged from industrial grade Epsom matrix printers. The X and Y steppers have round frames. The latest stepper for the Z axis has a square frame.
The pulley wheel is about an inch in diameter with symmetrical teeth. It appears that there are at least two standards for this size of belt pulley pitch, the other having teeth narrower than the gaps between them. My problem is I do not have a belt small enough for this application. It needs to be between 80 - 90mm diameter. Until I find one I will not be able to mount the Z stepper motor.
6th October 2006
Fitted the Delrin drive 'nut' to the Z table and assembled drive rod. It now looks like this ...
As can be seen from the last photograph, there is plenty of room to fit the Z stepper on the rear of the plate. There will be a belt drive to the Z drive screw on the right. The bearing block under the pulley is bolted to the left X table vertical plate. There is actually a gap between this block and the Z table vertical plate. The steel Z drive nut is fitted to the back of this plate using the two Pan headed screws. The cutter motor and shaft will be mounted on this front plate. All of the main components were cut out using a jigsaw and hand finished with a file.
I think next I need to give some thought to the very important limit switches. Opto switches are one option but since most of the machine is built out of ali, I am wondering if I can get away with magnet operated reed switches. I don't have any software for this yet and I am not sure if it is normal to use the limit switches for homing purposes ?.
4th October 2006
Made up Z table and fitted to Y table. Used two cut down and re-worked steel drawer slides. Still have to fit drive nut to Z table. Tidied up various items, long screws etc.. A word of warning. When you shorten a slide there is nothing left to stop the slide running out of the track and then all the ball bearings fall out !.
2nd October 2006
Made new X table drive screw rod and 'fine tuned' table Delrin drive nut block to produce correct alignment with X stepper motor adaptor.
1st October 2006.
Direct dial modem card blew up during an electrical storm, causing computer to make expensive noises. Forgot to disconnect this card from the telephone line when I changed to Broad Band !.
28th September 2006
Next step was to fit an X table. The piece of ali plate from the scrap yard was really much smaller than I could have fitted, but since I can always change it later, I decided to use it. In the MDF version of the machine I had simply used two steel draw ball slides on their backs and must have got things just right because it gave a nice tight, smooth assembly. When translated into the ali version ... it wasn't so tight and the table was subject to a bit of play. I concluded that I needed to adjust the spacing of the two draw slides. It is a fact of life that only one flank of a screw is used in practice, same with bearings and slides. So to get zero backlash we usually need two drive nuts one bearing on one flank and the other on the other flank of the thread of the drive rod. When using steel ball bearing drawer slides we need to do the same. So my idea was to fix one slide .. and then move the other away from it so that the balls made solid contact with the outer bearing surfaces of the slides. I have decided to incorporate some means of adjustment, to this end. Probably by tensioning the slides apart while they are bolted into position.
I decided to make a new Delrin X table drive nut block, that is now done. Driving the rod with a drill showed that something was amiss and it turned out to be a bent 8.0mm drive rod. All of the 8.0mm studding I had in the workshop was also bent. The easy way to check it to place the studding on a smooth sloping flat surface and it should roll off. If it is not perfect then it will not roll.
I didn't actually 'design' this heap ... it sort of appeared in front of me Hi!. During construction I found I had to continually dismantle and re-assemble things, but it became obvious that the 'adjustment' of a few holes, component diameters etc .. would make this a lot easier. So I spent some time today in doing just that.
24th September 2006
I decided to make a completely new Y and Z assembly and finally settled on the inverted "L" configuration. The left end mounting block for the lower guide rod has not yet been fitted. This block will have four set screws to align the free end of the 16.0 mm guide rod. I will probably do that after the X table has been fitted. The three roller idea seems to work OK and it is possible to adjust it to zero backlash. I used two sealed flanged ball races in each roller. At the moment I have fitted a Delrin driver 'nut' on the Y table. It will be interesting to see how well it wears.
There is a ball race on the free end of all drive screw rods. At the moment I am planning to fit a handle on the end of the X and Y drive rods, which is the reason the X rod is taken to the front. If this machine works, I will probably remove the handles, shorten the X rod and use electronic 'nudge' buttons for manual use.
I have not bothered to tie myself down by making a plan. The base is the size it is because that is the size of plate I found at the scrap yard. The uprights and back panels are that width because that was the width of the scrap duct I cut them from.
The Z stepper will be mounted on the rear of the roller plate and will belt drive the Z screw. At the moment I am thinking of using two steel draw slides for both the X and Z tables
15th September 2006.
The Mark 4 Engraving machine.
Yes I know what I said !. However ... I thought I would have one last go and build one from ali this time. After the expensive mistake with the Mark 3, I decided to do this one on the cheap, so my first visit was to a scrap yard to see what ali they had. After three visits for replenishment purposes ... I have now spent the grand total of £5 on aluminum.
Since I did not have any bending facility, I bought scrap aluminum ducting as a box section and then split it using a jigsaw. This was used to create the two uprights and the back panel. The base is made of aluminum plate and angle. The two 16.0mm horizontal guide rods are structural and add to the rigidity of the assembly. I have no idea what frame size the stepper is, they came out of an old Epsom dot matrix printer and are about 56.0mm square. Only one horizontal guide rod is fitted at present, the other is sitting on the bed, along with one of the mounting blocks. The right hand mounting block is 'fixed'. The block at the other end will be adjustable for the final setting up. The The Y and Z assembly slides on two phosphor bronze sleeve bearing, mounted in home made blocks. This lower guide rod carries the total weight of the Y and Z assembly. The upper guide rod, is simply that, and will run between three delrin rollers (one of which is shown on the bed). Not shown is a horizontal plate that will be mounted on the rear of the Y and Z table. The 3 upper guide rollers and the Z stepper motor will be mounted on this plate. I have not really thought that part out yet.
The thing sticking out the top of the X and Y assembly is an XXL (?) belt pulley on the end of the Z drive screw. The X and Y drive screws and fittings are made up but not fitted yet. The mounting bracket for the X drive stepper motor can be seen on the rear of the bed.
I intend to use the Quasar 3158 - PC / Standalone Bi-Polar Stepper Motor Driver boards and mount them behind the rear reinforcing plate ... although I may change my mind and house them underneath the bed, depends upon how hot they run. These boards will drive 5 - 50 volt steppers, have opto isolation on inputs and all the logic to connect direct to a printer port. This means. The built in logic will allow 'nudge' switches to be mounted on the machine so it could operate as 'stand alone', ie a manual mill.
The cutter motor mounts directly onto the cutter shaft. I may change that, in fact I may build a completely different Y and Z assembly, now that I have a better idea of what I want.
4th November 2005
The Mark 3 Engraving machine.
I have been to a local sheet metal company this morning and arranged for the sheet steel components to be made for the mark 3 machine frame. After making the decision to change the lead screws from 6.0 mm to 8.0 mm, I have now turned up all the extra parts needed for the new lead screws.
When I received the metalwork, I found that most of the folds had been done on the wrong edges !. There was no simple way to salvage the metalwork and so I scrapped it, and promised to shoot myself if ever I tried to make an engraver again !.
5th June 2005
The Mark 2 Engraving machine.
I constructed the basic frame of the machine from MDF. The theory was that I had no way of cutting any material with any precision ... but the local DIY shop could cut MDF to size, with a reasonable accuracy. The end result was certainly rigid enough for the purpose, however there are problems when one wants to bolt steel assemblies to MDF as it is very easy to crush it. In the end I decided MDF wasn't the answer I was looking for. So I decided to scrap the basic MDF frame and replace it with steel. Also you can see I am using four bearings on the mark 2 Y/Z slide assembly and it made sense to change this to two sleeve bearings on the lower guide rod only. The theory being that it was easier to line up two bearings rather than four. Two ball bearings keep the Y/Z assembly in line on the upper guide rod. Lots of printers use this method.
Click on the thumbnail to see the full sized picture. Front view.
Top view of the Y/Z assembly. The Z axis stepper is not mounted on this photograph but will be to the rear of the assembly. In the Mark 3 machine, the upper sleeve bearings will be replaced by two ball races.
A standard Computer PSU modified by adding a load resistor and terminal block. A Quasar stepper motor driver board is also shown.
The steel frame.
Since I do not have the means to cut the components out of 2.5 mm sheet and bend them, I decided to get the parts made by a local sheet metal company. I am still waiting !.
The frame will consist of four sheet steel components with a 15.0 mm lip (return) on two opposing edges and will replicate the MDF style of frame. I decided to keep the 'moving hole' idea from the Mark 1 machine as this will make it very easy to set up to the required accuracy. All of the turned parts required to make the change have been completed.
Both the Mark 1 and 2 machines used 6.0mm studding for the drive screw rods. I still think that 6.0 is perfectly adequate but have decided to change to 8mm for the next machine, giving a pitch of 1.25 mm instead of 1.00 mm. This may mean that I will have to make a completely new Y/Z assembly.
24th July 2003
The Mark one milling machine.
|X Table Frame. Table missing.||
Lead screw bearing housing (8mm) and mobile hole nut.
|Rear of Y Table. Upper bushes missing.||X and Y tables assembled. Z table missing.|
|Mobile hole nuts for X and Y guide rods. (1/2").||
Z Guide rod collars (3/8"). Not yet welded in position .
Stepper motor links.