Michael G
19th August 2012, 09:05 PM
I said that I would write up the job I wanted to get the 5mm slitting saw for at a later date. The saw was ordered but hadn't arrived so I used a 3/16" and did two passes - annoying but that's the way it goes.
Bryan popped in on the way to somewhere to drop off some gear and saw the brutal part with the hammer, but didn't get to see the rest of the job (that is, the non-hammer parts). I was actually making up change gears. I could buy a solid piece of material but that would cost a fair bit and for a change gear that is really a waste as there is not much power being transmitted. Instead I do it like this.
I start with a piece of square bar (in this case 20x20mm) and take it down in one dimension to a little over (say 1mm) the width of the desired finished gear (5/8")-
219935
Having done that, I set up the bandsaw and cut a series of pieces all of the same length but with a 15 degree angle on the end. The length is determined by the finished gear diameter plus some clean up. These two are spares as I cut 12 pieces + a couple of extra. Handy for set up trials, gauging and all that. These have also had the slot put in (5mm deep, 5mm wide - can sometimes need to be wider depending on the plate) and have been weld prepped
219936
The marker pen line on the side is important. Before cutting I put a line down one side of my bar stock. To guard against the saw being out of alignment I then arrange the blocks in a way to minimise this effect.
Once I have the blocks cut and grooved and prepped, they are arranged around a plate (nominally 5mm thick) cut with 12 sides to match the block recess dimensions. I find a thin cutting disc in an angle grinder is the easiest/ quickest way of producing these shapes. The texta lines on adjacent pieces are orientated alternately on the top and the bottom of the base disc. The weld prep insures that even with some slight clean up, there will still be some weld holding the blocks onto the next block. Care is needed with welding as if heat is put in all on one side it may distort, so I alternate symmetrically to try and keep things even. These two discs have been welded up and are ready for clean up -
219937219938
As well as welding the blocks to each other, I also attach the blocks to the base disc with a small fillet on alternate sides. A full length weld is not necessary. The next stage for these two discs will be clean up with the angle grinder and then in the lathe. Once I have a round disc with a centre it is just a matter of mounting in the dividing head and cutting the teeth (gaps). The larger disc with the rule across it is for a 127t 12DP gear (OD= 273mm - possibly the largest diameter gear I will ever cut). The smaller one is for a 100t gear (OD=216mm). I usually allow the gear OD + say 2mm for clean up as the A/F dimension. Both gears will be mounted together so that I have a conversion gear pair (I'm yet to make and weld in a hub). The 127t gear has been made on a plate made of 5x50mm flat because the finished size will be around that but as well the widest piece of 5mm plate I had was 200mm wide.
In the best cooking show parlance, here's one that I prepared earlier. The dished hub on this one is for mounting on the mill (this is also 100t). As you can see they clean up well enough.
219939
The critical bit is how the blocks fit together. I don't have an oxy set, but if someone wanted to, they could probably braze the blocks onto the plate and the joints in between. It took a while to find a bad one, but this a joint on that 100t gear where the fit up isn't 100%. See how top and bottom there is still some weld due to the prep. One day if I'm feeling keen I may fill this with the TIG and file it back but it hasn't caused problems so far.
219940
And why 12 blocks? I found this was a nice balance between the amount of extra material that would have to be removed if I used less and the extra mucking around that more would cause. These days anything I want to mount in the lathe that is not round I'll put 12 sides on it if I can. As well, 12 is divisible by both 3 and 4 which can help if you are trying to mount in a chuck for clean up.
Michael
Bryan popped in on the way to somewhere to drop off some gear and saw the brutal part with the hammer, but didn't get to see the rest of the job (that is, the non-hammer parts). I was actually making up change gears. I could buy a solid piece of material but that would cost a fair bit and for a change gear that is really a waste as there is not much power being transmitted. Instead I do it like this.
I start with a piece of square bar (in this case 20x20mm) and take it down in one dimension to a little over (say 1mm) the width of the desired finished gear (5/8")-
219935
Having done that, I set up the bandsaw and cut a series of pieces all of the same length but with a 15 degree angle on the end. The length is determined by the finished gear diameter plus some clean up. These two are spares as I cut 12 pieces + a couple of extra. Handy for set up trials, gauging and all that. These have also had the slot put in (5mm deep, 5mm wide - can sometimes need to be wider depending on the plate) and have been weld prepped
219936
The marker pen line on the side is important. Before cutting I put a line down one side of my bar stock. To guard against the saw being out of alignment I then arrange the blocks in a way to minimise this effect.
Once I have the blocks cut and grooved and prepped, they are arranged around a plate (nominally 5mm thick) cut with 12 sides to match the block recess dimensions. I find a thin cutting disc in an angle grinder is the easiest/ quickest way of producing these shapes. The texta lines on adjacent pieces are orientated alternately on the top and the bottom of the base disc. The weld prep insures that even with some slight clean up, there will still be some weld holding the blocks onto the next block. Care is needed with welding as if heat is put in all on one side it may distort, so I alternate symmetrically to try and keep things even. These two discs have been welded up and are ready for clean up -
219937219938
As well as welding the blocks to each other, I also attach the blocks to the base disc with a small fillet on alternate sides. A full length weld is not necessary. The next stage for these two discs will be clean up with the angle grinder and then in the lathe. Once I have a round disc with a centre it is just a matter of mounting in the dividing head and cutting the teeth (gaps). The larger disc with the rule across it is for a 127t 12DP gear (OD= 273mm - possibly the largest diameter gear I will ever cut). The smaller one is for a 100t gear (OD=216mm). I usually allow the gear OD + say 2mm for clean up as the A/F dimension. Both gears will be mounted together so that I have a conversion gear pair (I'm yet to make and weld in a hub). The 127t gear has been made on a plate made of 5x50mm flat because the finished size will be around that but as well the widest piece of 5mm plate I had was 200mm wide.
In the best cooking show parlance, here's one that I prepared earlier. The dished hub on this one is for mounting on the mill (this is also 100t). As you can see they clean up well enough.
219939
The critical bit is how the blocks fit together. I don't have an oxy set, but if someone wanted to, they could probably braze the blocks onto the plate and the joints in between. It took a while to find a bad one, but this a joint on that 100t gear where the fit up isn't 100%. See how top and bottom there is still some weld due to the prep. One day if I'm feeling keen I may fill this with the TIG and file it back but it hasn't caused problems so far.
219940
And why 12 blocks? I found this was a nice balance between the amount of extra material that would have to be removed if I used less and the extra mucking around that more would cause. These days anything I want to mount in the lathe that is not round I'll put 12 sides on it if I can. As well, 12 is divisible by both 3 and 4 which can help if you are trying to mount in a chuck for clean up.
Michael