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Best wood for pole blocks ?

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#1 mantrain

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Posted 20 February 2013 - 03:33 PM

a close look at my blocks reveal that they are the crude obsession version --

http://s1224.beta.ph.../biggdaddyne...

But now I want to make new blocks, the obsession ones. Several times I tried but the blocks kept on splitting, and I gave up. I think I was using cherry wood, and perhaps it was the wood more than my technique, because even the ones I have occasionally split. So, when making the new blocks can someone recommend the best type of wood for this project?
thanks!

#2 StarStuff1

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Posted 20 February 2013 - 03:45 PM

A tough fine grained hardwood would be my recommendation. I have made good blocks out of ash. Probably some other woods as good or better. Many woodworking/telescope makers here so I am sure you will get some excellent ideas.

#3 Pinbout

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Posted 20 February 2013 - 03:45 PM

for $150 used amart add

aurura precision sells plastic blocks

and moonlite

#4 Steven Aggas

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Posted 20 February 2013 - 04:27 PM

I made some out of Cherry for my 20". They still look great after 20 years. I made a set out of Ash for the 36", painting them black, and 7 years later still going with no problems.

Best,
Steven

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#5 Jeff Morgan

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Posted 20 February 2013 - 04:30 PM

for $150 used amart add

aurura precision sells plastic blocks

and moonlite


I've tried numerous times with wood (oak and mahogany), and they inevitably split. Wasted lots of wood and lots of time. If I were to try again, I would use plywood laminated to the needed thickness.

Better yet, go commercial, aluminum or delrin! Wood just isn't the right material in terms of longevity or attachment flexibility.

#6 mantrain

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Posted 20 February 2013 - 04:51 PM

for $150 used amart add

aurura precision sells plastic blocks

and moonlite


I've tried numerous times with wood (oak and mahogany), and they inevitably split. Wasted lots of wood and lots of time. If I were to try again, I would use plywood laminated to the needed thickness.

Better yet, go commercial, aluminum or delrin! Wood just isn't the right material in terms of longevity or attachment flexibility.


Perfect, I have plenty of plywood available!

#7 astrobeast1

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Posted 20 February 2013 - 05:01 PM

Maybe the problems you guys are having with wood blocks homemade is the main pole hole is drilled down the grain --it should be across the grain --hope this help,s

#8 JimMo

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Posted 20 February 2013 - 05:03 PM

Yes, Baltic Birch plywood would be great, but only the good stuff with many thin layers of hard wood, not the BB available at Lowes Depot.

That said, mine are made out of Maple and in seven years of service there are no problems whatsoever.

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#9 Achernar

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Posted 20 February 2013 - 07:54 PM

Use a dense hardwood such as Ash, Hickory Maple, White Oak or even Red Oak. If it's strong enough for baseball bats, tool handles, bowling lanes, ships and your Aunt's table top, it will make good pole blocks. I made mine from Red Oak, stained with Minwax Red Oak stain then topcoated with three coats of Minwax exterior polyurethane. I used the directions from the K&B book, with one exception, I made a sled that slides in the groves of my table saw's top, and I used a stop block and clamps to make the splits. To hollow out the back, I used a dado head on the table saw. That way my hands are away from the blade and the splits will be in the same places on all eight blocks. I chamfered the edges not against the mirror box with a 45 degree chamfer bit, and I did it with a jig that had two strips of wood in a "V" to hold it without jeopardizing irreplacable body parts. Drill the pole bores carefully to the same depth and drill them all with what will be the front or back facing you. That way, if the bore is canted slightly it will be consistent, there is nothing worse than truss poles canted inwards and outwards at the same time. When buying the wood, buy enough so you can laminate two or more layers together so you have enough thickness to make the blocks. I glued three layers of red oak with yellow wood glue, clamped and allowed them to bond for 24 hours. Then I used my planer, jointer and table saw to form them into a plank from which I cut out the blocks. Don't despair, I messed up the first time making them too, but got it right on the second try. Remember, drill the pole bore across the grain, make the splits across the bore and along the grain. Go the other way, and they will split. Mine have been in use for two years with no problems, in part because I not only made them to the Obsession standard, there is more wood between the face of the blocks and the pole bore.

Taras

#10 JohnH

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Posted 20 February 2013 - 09:07 PM

In the course of building my 12 1/2", I experimented with various woods to see how they would fair.

My first ones out of oak wouldn't hold well and split along the grain when forced.

The ones out of maple and cherry did better but don't stain as well unless immersed (quite practical for small things like this) in the stain.

I did mine quite simply: a hole with a connecting slot an a 3 pronged nut will be quite tight with only a small plastic nut glued onto the 1/4" X 20 bolt.

#11 Bill Kocken

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Posted 21 February 2013 - 09:19 AM

I'll ditto the laminated plywood. It tried making them out of oak and it was a dismal failure because oak isn't the right wood to being with, but I made 2 other stupid mistakes. First, I made them all at once, assembly line fashion before testing any. Second, I drilled the hole with the grain which made the clamping tab go across the grain. ( see Jim M's picture for the proper direction.) After all that, and burning up a forstner bit, they cracked immediately. Epic fail!

I was very frustrated, so I laminated up some nice baltic birch. I bored the hole all the way through and made a single slit style clamping block. To get them to point correctly upon installation, I attached them loosely and shimmed them.

By the way, our club's 30" Obsession (and maybe the 25" as well) use laminated plywood instead of maple for the blocks.

#12 JohnH

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Posted 21 February 2013 - 09:33 AM

I made my maple blocks out of 7/8" thick stock, about 1 1/4" by 3" long.

To test them, I clamped it a 3/4" iron pipe around 2 feet long and clamped it into my metalworking vise.

At about 20 lbs of force, the wood split next the the clamp and I guessed that a 5 lb cage distributed over 3 clamps had an adequate saftey margin.

#13 ausastronomer

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Posted 21 February 2013 - 05:32 PM

If you want to use timber then laminated plywood is the only way to go. The multiple layers with the alternate grain pattern is far better suited, than any single piece of timber, to the continual flexing the blocks are subject to.

However, plywood like all timbers can shrink and expand. This usually doesn't cause too many problems but I have seen on rare occasions a few 25" Obsessions where the guys couldn't get the poles in the blocks in really damp humid conditions.

Without question the best material for pole split blocks is delrin. It will last forever and isn't sbject to weather in any way.

An image of the Delrin split blocks on my 14 inch SDM is below. They look good and work beautifully.

Peter Read at SDM telescopes went from Obsession style plywood laminated blocks a few years back and said the delrin is way better and easier to work with. It is a good bit more expensive and you may find it difficult to buy the small amount needed.

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#14 Gordon Rayner

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Posted 21 February 2013 - 06:08 PM

Have you tried PVC? I have worked much with Delrin. Pricey in the thickness you show. PVC does not machine as well as Delrin or Celcon, but it can be done.

#15 ausastronomer

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Posted 21 February 2013 - 08:08 PM

Hi Gordon,

No haven't tried PVC. Delrin is pricey but when applied to the cost of a large scope it's small.

The material for 8 Delrin blocks is about $100. A premium 20" plus scope with all the toys leaves very little change out of $20k, if any. Unfortunately of course a hundred here and a hundred there all starts to add up very quickly. It does do a superb job and IMO is well worth the cost.

Cheers,

#16 Achernar

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Posted 21 February 2013 - 09:32 PM

It's no suprise those blocks failed immediately because the pole bore drilled along the grain weakened them greatly. I can tighten the knobs on my 15-inch's pole blocks firmly and I can see the middle section deflect ever so slightly. The pole bores were drilled at right angles to the grain, not along it. Each one is fastened to the mirror box with four stainless steel 1/4"X20 2 1/2" machine screws, one in each corner. If however the poles were long or larger in size than the 1-inch tubing I used, I probably would have used another way to attach the poles.

It hadn't occured to me to use Delrin to make pole blocks, but if they are stronger than hardwood or plywood, they have a clear advantage. Sometimes it is hard to get the poles into the blocks when the humidity is high, whereas Delrin is unaffected. I wonder if standard wood working tools would work on Delrin, or would it require machine tools in order to make good pole blocks.

Taras

#17 whirlpoolm51

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Posted 22 February 2013 - 09:56 AM

i second delrin and pvc i have made direct copies of moonlites truss connectors out of pvc and they work great!!

a sheet or block of pvc stock isnt that expensive at all and way cheaper then delrin.

I would go with one of those for the best outcome, Just have a look on ebay

type in delrin stock or pvc pipe then look for pvc sheet,block,rod etc etc






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