Its now time for the reality check. After building a LOA that looks OK from the distance its time to fix the bits that just are not good e.g.
1. Lateral support is going to be required as for the most part its only small corners of the mirror box that are holding the Alt beams in place. As you move to Horizontal, lateral support gets less or non existant.
There is always the option to build a thin board on the inside of the Alt Beams however I am going for four vertical blocks spaced at 1/3 distance ( 2 each side).
2. The Alt Beams are going to require support towards the end of the large radius, particularly when the scope is moved towards horizontal.
3. You may notice a big chunk out of the top end of one of the beams. The result of not leaving enough room when routing two beams on the one sheet.
4. Sanding and general tidy up required on all surfaces to make up for not optimal woodwork when cutting, gluing and screwing. Should use a table saw for more accurate alignment for a start.
Great to see your progress and it looks great. Have you thought about using a flex rocker? It would suit the large bearings you have and lead to a lighter overall design. There is a picture of one in the Albert Highe book.
Thanks Rod and others who have offered suggestions. As a first build I am opting for more traditional dimensions and design. The "Flex rocker" does look interesting, doing away with the mirror box entirely (very minimalist).
Today I trimmed the tip of the Alt Bearings and gave them a simple brace with a dowel join at each end. Along with the Lateral support blocks on the rocker it has a far more secure feel moving from Azimuth to Horizon.
Kunama (Matt) also suggested the use of felt pads as gliders to stop excess movement. Sounds like a great idea.
Just to clarify. The flex rocker refers to the rocker and base ring. You can still use a mirror box. I have a mirror box with mine. Here is another example:
Neil, re the felt pads placed between the mirror box outside and rocker box inside will prevent excess side to side movement. The alt bearing itself will need to be surfaced with some laminex and then glide on teflon pieces attached to the rockers.
I went to the local Laminex Group warehouse and managed to get some nice discontinued laminate . I also scored a half sheet of discontinued post forming laminate in black. Total cost: $40.-
The post-forming laminate is actually just under 0.8mm so about half the weight of normal laminates. I will be getting the belt sander out and taking another 10th off it and then will use it for the UTA light baffle.
Regarding your alt bearings, if you still get too much flex in them, try a wider piece between the two sides.
Secondary cage rings completed, NOW how to connect all of this?
Have to order threaded inserts for aluminium tubing and find matching screws and washers to connect the four secondary cage tubes for a start.
Neil, the threaded inserts or star nuts are available in a few sizes, depending on the inside diameter of your tube. You can search on eBay for star nuts.
Bicycle shops also sell them (but double the price) as they are used in the steerer tube on bike forks.
Make sure they are not too small, they should in fact match the OD of the tube and then they will be a good fit inside the tube.
A cheaper alternative I have seen on some DIY stuff has been a short piece of tas oak dowel araldited into each end of the strut and then screws used instead of machine screws.
Matt
Sorry to be off theme however, i have been sending you some private messages and cant confirm that they are working as they don't appear in my private message sent list.!! Am i doing something wrong?
Hi Neil,
Just found one from yesterday, reply on its way..
(you can change your message settings to always keep a copy in settings)
Time to test joining the secondary cage rings with Araldited dowel in each end of the aluminium poles. Final version will be made of lighter 1/2 Ply and probably use spring threaded inserts, "star nuts".
Assembled the two rings just as a test. No glue, just a screw in the top of each tube through a dowel insert. This method alone would obviously not provide enough stability. Will use threaded inserts and build ply supports between the front and rear ring for the Focuser and Finder to add to the stability.
Also finding out drill bit diameters to countersink tubes. What I thought was 1 inch Aloy was closer to 28 mm.
Time to test joining the secondary cage rings with Araldited dowel in each end of the aluminium poles. Final version will be made of lighter 1/2 Ply and probably use spring threaded inserts, "star nuts".
Be very careful choosing any epoxy for as a construction adhesive. The epoxy called Atraldite and any of the ones sold at Bunnings are hydroscopic over time and will eventually fail in stressed joints. The only adhesive I use is proper boat building epoxy systems, the International HT9000 stuff is good and can be purchased at Whitworths and BCF. WEST System is good too but hard to find. Glue powders must be used in any resin mixture to be used as a glue or bonding agent.
Assembled the two rings just as a test. No glue, just a screw in the top of each tube through a dowel insert. This method alone would obviously not provide enough stability. Will use threaded inserts and build ply supports between the front and rear ring for the Focuser and Finder to add to the stability.
Also finding out drill bit diameters to countersink tubes. What I thought was 1 inch Aloy was closer to 28 mm.
Hi Neil,
I"m following your prototype closely, very enjoyable. I use star nuts to attach the tubes to the rings and they provide plenty of stability. Along with the focuser board attached with two screws at top and bottom and the tubes sitting in bored seats nothing will move.
Over here in North America, we have problems with varying tube sizes too, I now have 25mm, 1 inch, and 26mm forstner bits for drilling tube seats as the 1" tubes I order are not always exactly 1".
Keep up the good work, I see elements of Albert Highe's ideas in your prototype.
Last edited by starman345; 03-08-2015 at 11:02 PM.
Well this feels like the hard part.
1. Inside or outside mirror box mounting? just felt wrong and narrow when mounted on the inside of the mirror box.
2. Aloy brackets or traditional wooden blocks? for a first built I want to at least try low tech.
3. How was the removed section from the Alt beams required on two of the block mountings going to work?
4. Should I mount the blocks square to the mirror box and thus drill the required 1 1/4 inch holes at an angle OR simply twist the blocks the estimated 8% to 10% required so that they meet in the correct position on the secondary cage?
5. My test blocks were built from solid 2 x 4 and cut to size as outlined by Kriege and Berry except they are 2 inches thick not 1 3/4. Should they be made of two pieces of laminated Ply?
6. How thick should the split be to provide the required clamping effect?
7. What concession should be made to make them look more glamorous. Routed corners etc?
8. Used Pythagorus to estimate the 8%, 10% bracket angle required?
mmmmmm
1. I went with outside to keep the box smaller.
2. I used delrin, wooden ones can swell up with humid conditions.
3. If your cutting away for the block the bearing will obviously be a lot weaker, you can retain a lot of the strength if your clamp block is a tight fit in the cut out section.
4. I drilled the blocks at the angle but getting the angle right meant trying to remember sine, cosine and tangents again ...... I think next time I will get some round delrin, then it won't matter !!!
5. the extra thickness won't matter if you drill the hole off centre so the bit that has to bend is not too thick.
6 Depends on how tight a fit your truss is in the first place. With wooden block I would err on a looser fit with wider split. On the delrin, there will be no shrink/swell so a 2mm split is all I cut (cut on my slide/comp saw)
7. Route the corners, drill screws about 12mm in from corners and countersink.
8. the angle needs to be pretty spot-on or you will have to jiggle the pole a lot to get them in.
Not a convincing first look at the simplified split block.
I was using a softwood (possibly pine) 2 x 4 and the dimensions outlined in Krieg and Berry with the exception of using 2" not 1 3/4. As the picture shows I positioned the 1" bore closer to one side to make a thinner wall for clamping. The book example uses a 1 1/4" bore.
Performed a very basic hand saw to create the split and made it quite wide. 3 to 4 mm
The result is very little flex between surfaces.
1. Favours the use of the basic splilt-block socket which includes two splits an inch apart and the thinning of the middle section.
2. Use another wood, hardwood as advised.
I should add. This is table saw, drill press territory using a spade bit.
Ordered a set of Forstner bits to cater for the different diameters required in the build particularly the counter sinks that require a clean Flat bottom cut.
Today is version 2 of the Split Block.
I decided on truss pole diameter of 1 1/4 inches as I have been given three pool cleaning poles that may work. Out of these I should get 6 of the 8 struts required.
I obtained a 32mm spade bit that provided the correct cavity in the block for the Aloy poles.
Lessons to learn:
The hole through the block has to be perfect in vertical and horizontal orientation. The slightest inaccuracy will result in the truss not leaving the block at the correct angle to connect to the secondary cage. That is : its a Drill Press Job that i will have to complete in a friends workshead.
I was able to get more acceptable Flex with the wider diameter hole. It will still warrant having a look at the double split version.
I tested the use of M6 bolts and wing nuts to restrict the block.
My attempt at working through the double split-block sockets as outlined in Krieg and Berry.
Differs from the previous versions in that it uses a 1" channel 1/4" deep through the back of the block (that part facing the mirror box) and uses Two splits cuts horizontally not vertically along the visible side of the block.
The Nylon wing nuts I am using to test will not be robust enough. A considerable force has to be applied to clamp the thin channel of wood around the pole.
Still not excited by the result. Will have to keep testing.
Great to watch your progress. I made some split blocks several years ago using the version 3 style. I used a jarrah off cut to make the blocks. I don't know if that made any difference but they did seem to work well. I also used a large knob which helped grip the poles. I still have the blocks and knobs so can post some pics if that helps.
I did change the truss design after a few years to a one piece design like shown in the Highe book except I used 8 trusses not 6. I find this quicker to set up.
Your prototype is coming together quickly and looks great.
I admire your tenacity with the timber blocks Neil !!!!
I would recommend a harder timber, they will last longer and they will be less affected by changes in humidity.
I knew they would annoy me so I ordered some delrin ones from Cut To Size Plastics in Sydney. My blocks are 82x52x45mm and cost $6.05 each including GST. They are easy enough to drill but you do need a drill press and a TCT Forstner bit.
Happy with myself today! Found Ebony Star 50 laminate at the local bench top manufacturer.
