Post by springcrocus on Jul 12, 2016 16:12:11 GMT
After sitting at the end of the mill winding the handle for a very long time facing up a 12" length of black, flat steel I decided that a table feed was an essential extra. Although there are feed boxes available for my type of mill, they are around £300 each and as rare as hen's teeth and, unless I'm missing the obvious, don't have automatic disengagement. After spending a couple of days trawling the internet and watching endless youtube videos, I decided to make my own based around a windscreen wiper motor. So, once again, here is a start-to-finish description of how I sourced the parts and then built up my power feed.
As made, this project will work directly with a Warco WM-16, Chester 20V, Amadeal AMA25LV and SPG SP2217-III which all use the same 700mm x 180mm table, and is easily adaptable to mills of other sizes. Total cost of bought-in parts was under £30, everything else came from the scrap box.
To make a useful power feed five things are needed; a motor, a way to mount it, a power supply, some sort of speed control and a means to engage and disengage the drive.
The first item on the list was purchased from the local car breakers and cost £8. Although it doesn't seem to matter what vehicle it comes from, front wiper motors are larger than rear wiper motors, probably because they drive two blades. I'm told that mine came from an Audi A6.
On getting it back to the workshop, I hooked it up to my battery charger and tested it in both directions by swapping the polarity: it worked fine and the current draw was 2A under no-load conditions. This will probably rise to somewhere between four and eight amps when driving the table, especially if the table locks are lightly nipped up, and a power supply will be chosen or built once this figure is known. Meanwhile, a car battery and ammeter will suffice to get started.
The next thing to buy or make is a pulse width modulator (PWM) whose job it is to act like a dimmer switch and slow down the feed rate. This is just a simple device which generates a square-wave signal with adjustable mark-space ratio and applies this to one or more power transistors that provide power to the motor. These are easily made using the long-standing NE555 timer chip but I found some ready-built ones HERE on Amazon for £2.83 with free postage so two were ordered. They are not worth building at this price!
Before designing the motor mounting, I had to choose what sort of clutch arrangement I wanted and decided to use a sliding drive-dog layout that could be automatically disengaged by the machine using stops. The advantage of this is that if my attention gets diverted for any reason while a cut is running, the stops will ensure there is no disaster. After much internet research, and not finding exactly what I wanted, I decided to design my own system using a sliding brass sleeve arrangement that would work in both directions with a centre-off position. The framework for the motor and clutch would be mounted at the left-hand end of the table and the operating controls at the right-hand end where I always stand to wind the "X" axis handle.
To get started, I removed the M8 nut and washer holding the right-hand handle followed by the handle itself. This revealed a key set into the shaft which was also removed and put away safely with the other parts. The next item on the shaft is a thrust bearing and this needs to be retained in place and a way found to adjust the pressure on it. This function was previously undertaken by the Nylock nut on the end of the shaft.
Measuring the shaft showed it to be 10mm dia and a sleeve was designed to fit this and become both the bearing adjuster and the drive mechanism for the table. It is a 40mm length of 1/2" hexagon mild steel which is drilled and reamed 10mm to a depth of 20mm and the balance drilled and tapped M8. The sleeve is screwed onto the shaft and adjusted until it just locks the table, then backed off a tiny amount and a grub screw fitted in the end of the sleeve acts as a locking device.
The wiper motor has a knurled and angled face with an M8 threaded section so this was dissassembled and put in the lathe so that a 10mm dia spigot could be machined on it. For this, the sleeve is 25mm long with a 10mm dia hole reamed to a depth of 10mm and the rest tapped M8. There is also an 8mm wide undercut on the O/D machined to the root of the hexagon and the reason for this will become obvious later. The grub screw in the end is still needed to ensure that the sleeve doesn't unscrew itself from the shaft when going in reverse.
The motor mounting was now started and the main requirement was to get the ends of the two shafts in line and about half a millimeter apart, the idea being that a sliding collar can connect the two. After working out the PCD for the motor mounting holes, a piece of aluminium plate was sawn and then drilled to suit followed by the bolting on of the motor. This assembly was then offered up to get some idea of spacings. It obviously needed some way of being connected to the table and this meant that some fixing holes had to be placed in the table end-plate. A piece of 25mm x 3mm steel angle was chosen as the starting point and a 150mm length was drilled with a pair of 5mm clearance bolt holes and a relief section milled away to clear the leadscrew boss on the end-plate. The end-plate itself, which is made of cast iron, was drilled and tapped with two M5 holes in corresponding positions.
At this point, I decided to discard the first motor mounting plate and, instead, made a frame from some more of the steel angle. Hole positions for joining the pieces together were first calculated and these were drilled M5 clearance or drilled and tapped M5. The end piece also had a pair of M6 clearance holes drilled to mount the motor. Everything was assembled and it was obvious that some adjustment in all three planes was neccessary and most of the clearance holes were made into slots instead.
Now it became relatively easy to adjust everything and get the two hexagons exactly in line. The only downside at the moment is that the motor only has two orientations for mounting, sticking up in the air if mounted to the rear or with the motor to the front of the mill but I believe there are other motors that are the opposite hand, which would place the motor rearwards whilst remaining horizontal, and I may try and find one.
Now I needed to find a source for the sleeve and an internet search for "hex hole sleeve" at first looked promising. However, chasing down each of the hits in turn, it soon became clear that I would have to make my own. Not an easy task with my limited machinery, but a length of 1" diameter brass was faced to 48mm length and then set up vertically on the mill table. Using the bolt hole circle formulae from the Zeus book, and allowing for the size of the drill, a series of six holes were drilled through the block using a long-series 2.5mm drill. These form the points of the hexagon.
The block was then returned to the lathe and the centre was removed using a 1/2" drill that I reground to have a 90 degree point angle. This was to ensure that the drill followed the centre of the workpiece and didn't get deflected by the six corner holes. At the same time, a 1/4" wide undercut was made in the bore 1/4" in from the front and to just below root diameter.
A piece of the hexagon bar was cut about 2" long and a 1/2" dia spigot put on the front, the idea being to use this as a broach in the vice. It worked - just - but wasn't very good and the hole was cleaned up with files instead. The broach came in handy as a gauge, though.
Everything was now assembled, with the motor mount adjusted until the hexagon sleeve slid smoothly along the drive and driven shafts and the PWM was wired up to provide variable speed. As there was no mechanical means of moving the sleeve at this stage, it was engaged by hand. Everything worked as expected and I was able to control the feed from a dead stop to the equivalent of a fast turn by hand.
At this point, I have a usable power feed mechanism but there are still all the controls, stops and wiring to be sorted out.
Steve
As made, this project will work directly with a Warco WM-16, Chester 20V, Amadeal AMA25LV and SPG SP2217-III which all use the same 700mm x 180mm table, and is easily adaptable to mills of other sizes. Total cost of bought-in parts was under £30, everything else came from the scrap box.
To make a useful power feed five things are needed; a motor, a way to mount it, a power supply, some sort of speed control and a means to engage and disengage the drive.
The first item on the list was purchased from the local car breakers and cost £8. Although it doesn't seem to matter what vehicle it comes from, front wiper motors are larger than rear wiper motors, probably because they drive two blades. I'm told that mine came from an Audi A6.
On getting it back to the workshop, I hooked it up to my battery charger and tested it in both directions by swapping the polarity: it worked fine and the current draw was 2A under no-load conditions. This will probably rise to somewhere between four and eight amps when driving the table, especially if the table locks are lightly nipped up, and a power supply will be chosen or built once this figure is known. Meanwhile, a car battery and ammeter will suffice to get started.
The next thing to buy or make is a pulse width modulator (PWM) whose job it is to act like a dimmer switch and slow down the feed rate. This is just a simple device which generates a square-wave signal with adjustable mark-space ratio and applies this to one or more power transistors that provide power to the motor. These are easily made using the long-standing NE555 timer chip but I found some ready-built ones HERE on Amazon for £2.83 with free postage so two were ordered. They are not worth building at this price!
Before designing the motor mounting, I had to choose what sort of clutch arrangement I wanted and decided to use a sliding drive-dog layout that could be automatically disengaged by the machine using stops. The advantage of this is that if my attention gets diverted for any reason while a cut is running, the stops will ensure there is no disaster. After much internet research, and not finding exactly what I wanted, I decided to design my own system using a sliding brass sleeve arrangement that would work in both directions with a centre-off position. The framework for the motor and clutch would be mounted at the left-hand end of the table and the operating controls at the right-hand end where I always stand to wind the "X" axis handle.
To get started, I removed the M8 nut and washer holding the right-hand handle followed by the handle itself. This revealed a key set into the shaft which was also removed and put away safely with the other parts. The next item on the shaft is a thrust bearing and this needs to be retained in place and a way found to adjust the pressure on it. This function was previously undertaken by the Nylock nut on the end of the shaft.
Measuring the shaft showed it to be 10mm dia and a sleeve was designed to fit this and become both the bearing adjuster and the drive mechanism for the table. It is a 40mm length of 1/2" hexagon mild steel which is drilled and reamed 10mm to a depth of 20mm and the balance drilled and tapped M8. The sleeve is screwed onto the shaft and adjusted until it just locks the table, then backed off a tiny amount and a grub screw fitted in the end of the sleeve acts as a locking device.
The wiper motor has a knurled and angled face with an M8 threaded section so this was dissassembled and put in the lathe so that a 10mm dia spigot could be machined on it. For this, the sleeve is 25mm long with a 10mm dia hole reamed to a depth of 10mm and the rest tapped M8. There is also an 8mm wide undercut on the O/D machined to the root of the hexagon and the reason for this will become obvious later. The grub screw in the end is still needed to ensure that the sleeve doesn't unscrew itself from the shaft when going in reverse.
The motor mounting was now started and the main requirement was to get the ends of the two shafts in line and about half a millimeter apart, the idea being that a sliding collar can connect the two. After working out the PCD for the motor mounting holes, a piece of aluminium plate was sawn and then drilled to suit followed by the bolting on of the motor. This assembly was then offered up to get some idea of spacings. It obviously needed some way of being connected to the table and this meant that some fixing holes had to be placed in the table end-plate. A piece of 25mm x 3mm steel angle was chosen as the starting point and a 150mm length was drilled with a pair of 5mm clearance bolt holes and a relief section milled away to clear the leadscrew boss on the end-plate. The end-plate itself, which is made of cast iron, was drilled and tapped with two M5 holes in corresponding positions.
At this point, I decided to discard the first motor mounting plate and, instead, made a frame from some more of the steel angle. Hole positions for joining the pieces together were first calculated and these were drilled M5 clearance or drilled and tapped M5. The end piece also had a pair of M6 clearance holes drilled to mount the motor. Everything was assembled and it was obvious that some adjustment in all three planes was neccessary and most of the clearance holes were made into slots instead.
Now it became relatively easy to adjust everything and get the two hexagons exactly in line. The only downside at the moment is that the motor only has two orientations for mounting, sticking up in the air if mounted to the rear or with the motor to the front of the mill but I believe there are other motors that are the opposite hand, which would place the motor rearwards whilst remaining horizontal, and I may try and find one.
Now I needed to find a source for the sleeve and an internet search for "hex hole sleeve" at first looked promising. However, chasing down each of the hits in turn, it soon became clear that I would have to make my own. Not an easy task with my limited machinery, but a length of 1" diameter brass was faced to 48mm length and then set up vertically on the mill table. Using the bolt hole circle formulae from the Zeus book, and allowing for the size of the drill, a series of six holes were drilled through the block using a long-series 2.5mm drill. These form the points of the hexagon.
The block was then returned to the lathe and the centre was removed using a 1/2" drill that I reground to have a 90 degree point angle. This was to ensure that the drill followed the centre of the workpiece and didn't get deflected by the six corner holes. At the same time, a 1/4" wide undercut was made in the bore 1/4" in from the front and to just below root diameter.
A piece of the hexagon bar was cut about 2" long and a 1/2" dia spigot put on the front, the idea being to use this as a broach in the vice. It worked - just - but wasn't very good and the hole was cleaned up with files instead. The broach came in handy as a gauge, though.
Everything was now assembled, with the motor mount adjusted until the hexagon sleeve slid smoothly along the drive and driven shafts and the PWM was wired up to provide variable speed. As there was no mechanical means of moving the sleeve at this stage, it was engaged by hand. Everything worked as expected and I was able to control the feed from a dead stop to the equivalent of a fast turn by hand.
At this point, I have a usable power feed mechanism but there are still all the controls, stops and wiring to be sorted out.
Steve
