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I have the problem of drilling and tapping the underside edges of the fork blades. This would allow me to bolt the blades down onto the matching 20mm aluminium base plate. The difficulty is in aligning all three components so that six, tapped holes align perfectly. The fork blades are about 30cm high with diagonal ends.
I started by carefully marking, center punching and drilling 4mm holes through the base plate using my small pillar drill for six 8mm bolts.
The fork blades wont stand up on end nor allow me to use the pillar drill. There isn't remotely enough room for the pillar drill head to fit over the fork blade while it is resting in the machine vice. The holes need to be square and accurately aligned or the bolts will just bind. I could stand the pillar drill on a folding workbench with the fork blades projecting upwards. Though I'm not sure how accurately vertical the blades would be clamped in the workbench jaws. Nor how level each jaw would be relative to each other. A straight edge and square would obviously help here.
I could replace the pillar pipe on the pillar drill with something longer to obtain more clearance with the blades standing up in the machine vice. Though I don't have an angle plate to use as a guide for perfect perpendicularity of the fork blades. Vertical accuracy is likely to be a bit 'iffy.'
Or, I might be able to clamp the fork blades down onto the cross slide of my lathe and feed it onto various drills held in the 3-jaw chuck. Squaring the job up to drill the lower edges of the blades would be fun. Though I could use a long straight rod in the chuck and use a square as a guide.
It might be possible to do the job by hand with the blades clamped vertically and the bottom level. Drilling the holes 4mm allowed me to spot through the base plate into the edge of the first blade with the same drill. The 20mm thickness of the base plate is quite a good drill guide and 4mm drill robust enough not to bend or wander.
Or, I could make a temporary guide and table for the pillar drill by screwing two pieces of 4"x4" to a temporary 'table' of 3/4" plywood for the pillar drill to sit on. The 4"x4"s would be clamped either side of a piece of 20mm plate before the plywood 'table' was screwed down. The fixed 4"x4"s would then rest on a folding workbench with the fork blade down between the workbench jaws then tightened. The drill's own swiveling table would be turned out of the way. The drill would then be centered over each dimple in turn and lowered into the edge of the blade to ensure the holes are nicely perpendicular to the fork blade. The fork blade would be pressed upwards against the underside of the plywood in the slot to ensure the squareness of the lower edge to the drill stand above.
It might be wise to drill the the holes in the second blade only after the first is finish drilled, tapped and bolted down. The spacing and squareness of the blades to each other is rather critical. So the PA housing can be clamped between the two blades and both carefully aligned with each other with a square. Followed by a hand held drill spotting through the base plate to make shallow holes in the bottom of the second blade. The second blade is then removed and inserted into the drill 'table' slot arrangement. To accurately drill the holes deeper in the edge of the second blade using the dimples provided by the spotting drill.
Later, it occurred to me that there is no need for a thick 'table' top nor even that one be fixed to the 4"x4"s. It just needs the fork blade to be flush with the tops of the 4"x4"s and firmly clamped at both ends before being rested on the folding workbench. With the fork blade extending down between the workbench jaws during drilling. The fork blades and 4"x4"s need only be inverted and placed on a flat surface to ensure all is flush before clamping. I chose 4"x4" because of the large surface areas at right angles to each other which should avoid any twist while simultaneously providing firm clamping. A couple of lengths of heavy angle would serve just as well for the drilling operation. They could even be clamped in the workbench jaws once the fork blade was lifted to be flush with the tops of the angle. It's odd how these alternative methods pop up if you just ignore the problem for a while.
The workshop is presently hovering at freezing point so not very comfortable to work in. Warming it with a fan heater might cause massive condensation on my tools.
I ordered and received another 30 furniture cap nuts in silver finish and have bought more studding ready to replace the existing "gold" finished fixings on the bearing housings. The silver nuts are closed at the hex sockets so won't show or bleed rust on the sawn ends of the studs. These nuts are also much longer in their threaded shanks, making them a stronger fixing.
I also plan to re-saw the ends of the bearing housing plates to make them all even and of exactly the same length. A simple end stop will have to be provided on the miter saw to ensure accuracy. The bearing housing plates were originally sawn with a jigsaw which was never perfectly straight in its cut. By the time the ends had been filed and sanded the lengths and squareness were no longer quite as good as I hoped for. Remember that the plates are compressed between the cast flanges of the large 2" axis bearings by 16mm studs and domed brass nuts. So squareness is highly desirable for even compression and alignment. Not to mention the cosmetic appearance of these highly visible butt joints.
Or, I could make a temporary guide and table for the pillar drill by screwing two pieces of 4"x4" to a temporary 'table' of 3/4" plywood for the pillar drill to sit on. The 4"x4"s would be clamped either side of a piece of 20mm plate before the plywood 'table' was screwed down. The fixed 4"x4"s would then rest on a folding workbench with the fork blade down between the workbench jaws then tightened. The drill's own swiveling table would be turned out of the way. The drill would then be centered over each dimple in turn and lowered into the edge of the blade to ensure the holes are nicely perpendicular to the fork blade. The fork blade would be pressed upwards against the underside of the plywood in the slot to ensure the squareness of the lower edge to the drill stand above.
It might be wise to drill the the holes in the second blade only after the first is finish drilled, tapped and bolted down. The spacing and squareness of the blades to each other is rather critical. So the PA housing can be clamped between the two blades and both carefully aligned with each other with a square. Followed by a hand held drill spotting through the base plate to make shallow holes in the bottom of the second blade. The second blade is then removed and inserted into the drill 'table' slot arrangement. To accurately drill the holes deeper in the edge of the second blade using the dimples provided by the spotting drill.
Later, it occurred to me that there is no need for a thick 'table' top nor even that one be fixed to the 4"x4"s. It just needs the fork blade to be flush with the tops of the 4"x4"s and firmly clamped at both ends before being rested on the folding workbench. With the fork blade extending down between the workbench jaws during drilling. The fork blades and 4"x4"s need only be inverted and placed on a flat surface to ensure all is flush before clamping. I chose 4"x4" because of the large surface areas at right angles to each other which should avoid any twist while simultaneously providing firm clamping. A couple of lengths of heavy angle would serve just as well for the drilling operation. They could even be clamped in the workbench jaws once the fork blade was lifted to be flush with the tops of the angle. It's odd how these alternative methods pop up if you just ignore the problem for a while.
The workshop is presently hovering at freezing point so not very comfortable to work in. Warming it with a fan heater might cause massive condensation on my tools.
I ordered and received another 30 furniture cap nuts in silver finish and have bought more studding ready to replace the existing "gold" finished fixings on the bearing housings. The silver nuts are closed at the hex sockets so won't show or bleed rust on the sawn ends of the studs. These nuts are also much longer in their threaded shanks, making them a stronger fixing.
I also plan to re-saw the ends of the bearing housing plates to make them all even and of exactly the same length. A simple end stop will have to be provided on the miter saw to ensure accuracy. The bearing housing plates were originally sawn with a jigsaw which was never perfectly straight in its cut. By the time the ends had been filed and sanded the lengths and squareness were no longer quite as good as I hoped for. Remember that the plates are compressed between the cast flanges of the large 2" axis bearings by 16mm studs and domed brass nuts. So squareness is highly desirable for even compression and alignment. Not to mention the cosmetic appearance of these highly visible butt joints.
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