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With the two, long term, offending birch trees now finally felled and sawn into logs I was free to spend the day working on the mounting. I can start erecting my intended observing platform once I have prepared the base.
First I used my miter saw to chop off the overhanging "Spock's ears" on the fork blades. The specialist 100 tooth [Aluminium cutting] saw blade cuts quite cleanly but picks up some aluminium in a couple of the tooth gullets each time. This produces a knocking sound which is fortunately not too alarming. Nor too damaging of saw cut quality. I use a sharp awl to carefully pick the hard packed aluminium out of each affected tooth. The maximum so far has been only three clogged teeth. With an average of two. Since I have no need of polished cuts I just persevere with the cut. Picking the teeth with the power applied, mid cut, is really not very sensible.
Each piece of aluminium plate to be cut is carefully fixed down onto the saw's cast 'table' with the supplied clamp. I then back that up with the 'toe' of an 8" C-clamp [G-cramp] caught under one of the "handles" in the saw's base casting. Naturally I only use just enough tightening effort to ensure the plate I am cutting stays securely in place during the cut. The sheer weight of each plate is halfway to being secure but I don't want my free hand holding the piece of metal in place!
DeWalt could usefully improve its work piece clamping arrangements. Or provide some reinforced clamping areas under the base casting. The post clamp always distorts in use but does seem reasonably secure. It just looks and feels horribly cheap and nasty for such an expensive tool! More of an afterthought by a designer who never cut anything in his life except slicing carrots for a salad.
Each piece of aluminium plate to be cut is carefully fixed down onto the saw's cast 'table' with the supplied clamp. I then back that up with the 'toe' of an 8" C-clamp [G-cramp] caught under one of the "handles" in the saw's base casting. Naturally I only use just enough tightening effort to ensure the plate I am cutting stays securely in place during the cut. The sheer weight of each plate is halfway to being secure but I don't want my free hand holding the piece of metal in place!DeWalt could usefully improve its work piece clamping arrangements. Or provide some reinforced clamping areas under the base casting. The post clamp always distorts in use but does seem reasonably secure. It just looks and feels horribly cheap and nasty for such an expensive tool! More of an afterthought by a designer who never cut anything in his life except slicing carrots for a salad.
The green Trefoflex cutting compound had no effect on cutting speed nor quality of finish. So I went back to adding kerosene [paraffin or lamp oil] with some light oil mixed in as a cutting fluid. It is easy to use a spare hand to dab the saw blade with an artist's paint brush during the cut. This usually causes some slight smoking downwind of the blade. The metal swarf flies forwards but I have deliberately not used the provided dust bag. Preferring instead to let the swarf fall onto the floor for easy sweeping up. Fortunately the swarf is coarsely granular rather than dusty. I use ear defenders when I am sawing in the shed. The noise seems much less when working out of doors. I will have to do some dismantling to clear away all the metal swarf before I start cutting wood for the observing platform.
I marked out and drilled two spaced holes on the inside, bottom plate of the Polar Axis housing. This was to accept an 8mm diameter, stainless steel U-bolt. I bought two of these from the boating department of a DIY superstore. The curve of the bolt will pass through a turnbuckle eye to provide slow motion adjustment in polar altitude. Tension will be the norm due to the balance of the declination axis and OTA around the polar axis altitude pivot.
I fitted a turnbuckle to my Fullerscope MkIV mounting and found it ideal for fine polar altitude adjustment. The applied loads are really quite low and the turnbuckle easily turned with my bare fingers.
I had bought the largest of the stainless steel turnbuckles on display for the new mounting but now realise I probably needed the smallest. A similar U-bolt will be fitted to the front plate of the polar axis support fork once I know the ideal location with a rather more suitable size of turnbuckle. In retrospect, a galvanized steel fencing turnbuckle would have been just as good. As it will be hidden well out of sight inside the box formed by the PA support fork and reinforcing plates.
The image shows the view between the fork blades through the missing base plate. The much shorter turnbuckle, I have now purchased, should reach a similar U-bolt in the base plate.
I had bought the largest of the stainless steel turnbuckles on display for the new mounting but now realise I probably needed the smallest. A similar U-bolt will be fitted to the front plate of the polar axis support fork once I know the ideal location with a rather more suitable size of turnbuckle. In retrospect, a galvanized steel fencing turnbuckle would have been just as good. As it will be hidden well out of sight inside the box formed by the PA support fork and reinforcing plates.The image shows the view between the fork blades through the missing base plate. The much shorter turnbuckle, I have now purchased, should reach a similar U-bolt in the base plate.
I sawed the unwanted triangles off the remaining length of 20mm x 200mm plate. The slanting ends were left when I cut the angles for each fork blade to rest on the base plate. I now have a neat but oversized rectangle of the heavy 13/16" x 8" alloy plate. Repeated trials followed with different overlaps of the base plate with the 11" RA wormwheel in place on a stub axle fitted into the lower PA flange bearing.
The bearing grub screws are handy to hold the wheel securely provided the applied wormwheel weight does not move the whole bearing in its spherical housing. So I now use a stub of 2" diameter pipe instead of the earlier, and much heavier, solid brass stump. This keeps the wormwheel aligned without the bearing sagging completely out of line as it did with the heavier brass bar. The spherical housing and outer bearing race provides the self-aligning aspect of the bearing. This avoids binding and uneven wear with slight misalignment of the flange housings.
Next I need to drill the massive fork blades for threaded crossbars and furniture nuts. I am continuing to use the same clamping arrangements which I have used on the bearing housings. These have proved to be very secure for simple butt joints between aluminium plates. The tensioned rods [studs] prevent lateral movement of the clamped plates. The steel studs would literally have to sheer before the plate could move inwards. The fork blades are also clamping the Polar Axis at the heavy altitude pivot. This parallel clamping arrangement ensures remarkable stiffness of the butt jointed assembly without pinning or direct bolting between adjoining plates.
While the plated, hex-socket head, flanged, furniture nuts give a neat and slightly unusual appearance which I prefer to using normal nuts, bolts and washers. The depth of the threaded shanks of the furniture nuts probably provide greater security than normal nuts. The flanged heads are designed to avoid the nuts sinking into the usual hardwoods used for assembling furniture. Bed heads are commonly fixed to their bases with these fasteners.
Images to follow when I have obtained a new and much shorter turnbuckle, hopefully tomorrow. While I was cycling to the shops it suddenly occurred to me that I couldn't have a central turnbuckle. Not without blocking access to a central pivot bolt [or nut] on the base plate. I shall have to offset the short, hefty turnbuckle which I bought today. Or provide a suitable hook arrangement on the azimuth pivot bolt itself? A bent, drilled plate is all it really needs to carry the tension loads.
I have yet to decide how best to hold the fork blades to the base plate. There are considerable vertical loads, tipping and torque forces on the base joint. It would be a disaster if the joint gave way. Even flexibility is highly undesirable. The major problem is that the fork is not a fully closed box like the axis, bearing housings. Moreover, some of the surfaces are no opposing each other.
The bearing grub screws are handy to hold the wheel securely provided the applied wormwheel weight does not move the whole bearing in its spherical housing. So I now use a stub of 2" diameter pipe instead of the earlier, and much heavier, solid brass stump. This keeps the wormwheel aligned without the bearing sagging completely out of line as it did with the heavier brass bar. The spherical housing and outer bearing race provides the self-aligning aspect of the bearing. This avoids binding and uneven wear with slight misalignment of the flange housings.
Next I need to drill the massive fork blades for threaded crossbars and furniture nuts. I am continuing to use the same clamping arrangements which I have used on the bearing housings. These have proved to be very secure for simple butt joints between aluminium plates. The tensioned rods [studs] prevent lateral movement of the clamped plates. The steel studs would literally have to sheer before the plate could move inwards. The fork blades are also clamping the Polar Axis at the heavy altitude pivot. This parallel clamping arrangement ensures remarkable stiffness of the butt jointed assembly without pinning or direct bolting between adjoining plates.While the plated, hex-socket head, flanged, furniture nuts give a neat and slightly unusual appearance which I prefer to using normal nuts, bolts and washers. The depth of the threaded shanks of the furniture nuts probably provide greater security than normal nuts. The flanged heads are designed to avoid the nuts sinking into the usual hardwoods used for assembling furniture. Bed heads are commonly fixed to their bases with these fasteners.
Images to follow when I have obtained a new and much shorter turnbuckle, hopefully tomorrow. While I was cycling to the shops it suddenly occurred to me that I couldn't have a central turnbuckle. Not without blocking access to a central pivot bolt [or nut] on the base plate. I shall have to offset the short, hefty turnbuckle which I bought today. Or provide a suitable hook arrangement on the azimuth pivot bolt itself? A bent, drilled plate is all it really needs to carry the tension loads.
I have yet to decide how best to hold the fork blades to the base plate. There are considerable vertical loads, tipping and torque forces on the base joint. It would be a disaster if the joint gave way. Even flexibility is highly undesirable. The major problem is that the fork is not a fully closed box like the axis, bearing housings. Moreover, some of the surfaces are no opposing each other.
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