Making an Alt-Az mount and Tripod
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I have made
several tripods for antique telescopes, and hopefully others may benefit from my
experiences. I made an alt-az mount along with one of the tripods, so it is
included in this article. I took the features I liked best from several of the
tripods for this article, so some of the pictures may not look exactly like the
text describes them.
Part 1. THE ALT-AZ MOUNT
I searched the Internet for pictures of alt-az mounts. Some
were too expensive to make for the client, and some had unwanted/unneeded
features. I then took the rest and made a drawing of what I considered a
combination of the best features, which was sent to the client. Then I started
looking for brass – not as easy as you would think. I ended up having to order
it from 3 sources. I laid out the patterns on cardstock, cut it out, and
transferred to the ½” sheet brass. I cut it out on the bandsaw, and machined the
straight edges, and sanded the curved edges with a drum sander. I machined a
hole in the base for a large bolt. The tube measured 4”, so I bought round brass
tube with 4” I.D. I cleaned it up in the lathe, turning the inside enough to
leave room for felt lining. Then I put the tube in the vise on the milling
machine and milled 6 slots for bolts, and drilled and tapped the holes. I turned
the piece 90⁰, and milled two opposing holes in
the middle, which were then tapped ½”-20. Then the tube was cut in half on the
bandsaw. A light sanding and it was ready. I turned a piece of cedar to 4” O.D.
and put it in the clamshell to keep everything in place. Then I made two large
thumbscrews from brass and threaded the ends to match the holes in the side of
the clamshell. Stainless steel hardware was used to put the mount together.
Figure
1
- Milling a hole in sheet brass
Figure
2
- Cleaning up the edges of the sheet brass
Figure
3
- Boring hole in center of base
Figure
4
- Pieces cut out, holes drilled, tapped, and countersunk for stainless steel
capscrews
Figure
5
- Cleaning up brass tube
Figure
6
- Squaring up the end of the brass tubing
Figure
7
- Milling slots in clamshell
Figure
8
- Cutting the clamshell in half – Note holes in sides 90⁰
from slots for Thumbscrews
Figure
9
- Machining the thumbscrews to hold clamshell to sides
Figure
10
- One thumbscrew made, cutting second.
Figure
11
- Aligning the pieces – note thumbscrews for sides of clamshell
Figure
12
– Putting mount together, lining up for test fit
Figure
13
- Mount on tripod. You can barely see the steel tripod top piece with bolt that
goes through the base to be held on by the nut. There is a large piece of Teflon© between the pieces which enables turning
the mount in azimuth.
Part 2 – TRIPOD Metal
Portion
Tripod top
I had a 6”
F15 Brashear with a rare crescent mount, but the tripod was long gone, or it was
mounted on a pier, I don’t know. Either way, I needed a tripod. This is a large
tripod, the legs are 80” long.
How to get
3 equally spaced and marked places to put the legs: I started with a piece of
steel plate. I turned it to the same diameter as the base of the mount, roughly
6”. To hold the legs, I used pieces of 1” x 2” rectangular thick wall steel
tube. I cut the tubing to 2” long, and drilled a ½” hole in the middle of each.
I took a pair of dividers and set one point in the middle of the circle and the
other exactly on the edge. Then holding the point on the edge, move the other
point to the edge, making a mark on both sides of where you started. Move the
point to the next mark and mark on both sides again. Continue on around, and you
will end up with 6 exactly spaced x’s on the edge of the circle. Then draw lines
from every other point to the middle. In my case I used 1” wide tube, so I
marked ½” on both sides of each of the 3 lines on the outside edge and inside.
Draw lines to connect the dots, and now you have outlines to put three 1” wide
tubes, equally spaced, on the edge of a circle, square with everything. I then
used c-clamps to hold them in place and welded them to the steel circle. Turn a
piece of steel to fit the space between the inside edges of the tubes 2“ long,
then bore a ¾” hole in it and weld to the plate and inside of the 1” x 2”
pieces. Beadblast, prime and paint three coats.
Figure
14
- Tripod top - Note the parts meet in the middle for added strength
Figure
15
- Third coat of paint applied; drying in the sun
Figure
16
- Machining top of tripod
Figure
17
- Machining piece for tripod top
Figure
18
- Turning tripod top bolt to O.D. for threading
Figure
19
- Threading tripod top bolt
Figure
20
- Checking fit of locknut
Figure
21
- Checking fit of tripod top with base bolt
Figure
22
- Bottom of tripod legs
Figure
23
- Looking at bottom of alt-az mount
Figure
24
- Completed tripod and alt-az mount with Cedar block to keep clamshell in place
Figure
25
- Closeup of alt-az mount on tripod
Figure
26
- Tripod with Alt-az mount and 4" refractor
Part 3 - Making The
Tripod Wood Legs
I am making
a set of Oak tripod legs for someone. I measured the legs on the 6” and the 4”
Clark tripods. The Oak legs I am making were in between the two sets, so I used
a 6” leg as a model, but shortened it. I cut the oak slightly longer and larger
than necessary to allow for sanding and final adjustments. I cut it 1-3/8” x 2”
x 70”. Then I made a taper jig for the tablesaw. (Internet has many ways to make
them.) The method I used was to lay out a full size pattern on a piece of scrap
wood. I cut another board 3” wide – in this section it is called “the 2nd
board”. To keep the grain running straight, you need to have the middle of the
pattern in line with the grain. I marked the distance – in my case, 1-1/4” from
the edge. I used a long straight edge and marked the middle. (You only need to
mark 2 or 3 inches on each end.) The 6” Clark legs are tapered just a bit on
top. I measured down 10” and made that the widest point. The tops are tapered so
all the wood will fit in the circle just below the top. I set the fence on the
table saw at 3” from the blade. (Arbitrary.) I measured 3” from the edge of the
2nd board to the outside taper line on the bottom of the leg. Then go
to the top and do the same, measure 3” from the outside edge of the 2nd
board to the outside line on the top of the leg. (If you need to center your
pattern with the grain, this is the time to do it.) I clamped it in place, then
pilot drilled holes and screwed the two together. If you don’t use pilot holes,
it is easy for a screw to bind in the Oak and break off when you’re trying to
remove it. Do the same for all 6 legs. Then I drilled 1-1/4” diameter holes ¼”
deep on one side of each leg in the middle, 2/3 of the way up from the bottom,
then turned a 1-1/4” dowel from the Oak, and cut it into three 1-1/4” long
pieces. Then I put the dowels in the holes and temporarily used a clamp to hold
the pieces in place. (When using clamps, use a thin piece of wood on each side
to keep the clamp from making marks on your project.) I used a long bolt/nut
through the top holes and 1-1/2” spacer between the top pieces to hold the legs
together side by side. I clamped the bottoms of the legs together and centered a
1” wide board to mark from bottom to where the board no longer touched the legs,
and cut that portion of each leg off using another jig on the tablesaw. I used
stainless and/or brass bolts, nuts, and woodscrews keep from rusting.
I made special bolts for the tripod top. Take it apart, round the tops,
round all the edges, stain if necessary, sand again, and polyurethane the legs
and dowel. Sand again and recoat.
I made 3 pieces of ½” steel, 5-1/2”
long. I turned one end to a point in the lathe. Then I drilled holes in the
bottom of the legs, maybe 4” deep. Put a pin in each hole, drill a hole through
the pin and use one of the ¼”-20 bolts to bolt it in. On one tripod, I put
threaded inserts in the bottom so the owner could change and use either sharp
points outside, or furniture tips inside on the floor. One tripod ended up with
brass barrel nuts and ¼” x 20 stainless steel threaded rod to hold the bottom
legs together. This gave a clean look, and the bottom bolt goes through the ½”
steel rod to hold it in place.
For a new
twist, the person getting the tripod just let me know they wanted a wood tray. I
normally use leather belts, so I had to design a tray. I tried triangle and
round, round worked out better. I used 3 pieces of 1” x 6” with shiplap joints
to make the 12” tray. I then glued a
plywood circle under the wood to make it stronger. I went through several design
phases before settling on pieces that hook over the 1-1/4” piece between the
legs. I made an aluminum circle piece and spaced 6 holes – three up and down,
three sideways. I threaded the holes ¼” -20 and used threaded rod to go to the
legs. I used 8-32 bolts to hold the piece to the bottom of the tray.
There was
some talk recently about making/buying appropriate tools to work on telescopes.
I have drawers full of screwdrivers, but even the largest one was too small to
screw in the inserts in the bottom of the tripod legs. I made what I needed.
Figure
27
Threaded inserts for bottom of tripod legs
Figure
28
Front view of custom made screwdriver blade
Figure
29
Side view of special made screwdriver blade
Figure
30
Custom made screwdriver blade in insert
Figure
31
Drilling holes prior to tapping
Figure
32
Tapping holes in ring
Figure
33
Eyepiece tray - bottom view showing how ring attaches
Figure
34
- Turning the 1-1/4" dowel
Figure
35
- Tops of the 6 legs before sanding
Figure
36
- Legs stained and with one coat of Polyurethane. Note the 1-1/4" recess for the
dowel.
Figure
37
– The three 1-1/4” Oak dowels
Figure
38
Temporary set up to make sure everything fits
Figure 39 Eyepiece tray for 2" eyepieces
Figure
40
Pieces to keep eyepiece holder in place, as well as to use as stretcher
Figure
41
Close-up of piece to hold eyepiece tray
Figure
42
Brushing Polyurethane on legs
Figure
43
Bottom of legs, showing one with rubber tips, one with tapered metal for outside
Figure
44 Belts I had made to keep
tripod legs from spreading apart. I also made the brass triangle to hold the
belts in the middle.
Figure -
45
Finished tripod with Brashear crescent mount and tube assembly
Figure
46
Completed tripod