Gina's Observatory Build - Abbreviated - Finishing Touches and Improvements

[Tinker1947]

Sounds to easy to me...

[Gina]

  We shall see    Looks alright though   In fact I think I may be able to get away with just 4 wheels.  With solid wheels an inch thick on nearly half inch axles I think these wheels should take the weight alright.  If they seem overloaded I can add one or two more but the problem then is getting any extra wheels to share the weight.  I over engineered it with the rubber tyred wheels - half of them aren't taking any weight

[Tinker1947]

Getting more than corner wheels to share the total weight of any roll-off roof would need the wheels to have suspension springs to share the weight, getting the roof level and then the v-groove level just won't happen there a lot of wood involved and it moves depending how much moisture it absorbs , so the wheel assemble would need a spring and a system to move up and down as it follow the v-groove, not to difficult but would take some time to sort out, the rubber tyres are not such a bad idea pneumatic would do the job with type pressure allowing the tyres to expand and contract with the uneven level of the v-groove....this drinking will thinking is interesting, the spell checker is working well...

[Gina]

I agree - anything more than corner wheels will either do virtually nothing or need suspension.  I think just two wheels a currently taking all the weight on each side.  I put 4 on the lighter north side and 5 (yes FIVE) on the south side.  I shall use just four corner wheels.

I've just remembered that I have some plastic wheels I bought first for my ROR before changing to the rubber tyred ones.  I think I know where they are but I don't know if I can get at them ATM.  They might well be acetal - don't know.  Can't remember how big they are - at least 75mm I believe.  I might be able to mount those on a mandrel and turn a V groove in the outside.

[Tinker1947]

Thinking about the V Channel getting it straight won't be to hard but keeping it straight will be down to the wood not moving like a bit of twist or warping, to get round this should it happen, the wheels could be fixed in place on the heavy side with shimms on the axles, but left to float on the south side so as the move along they can slide along the axle to stay in the centre of the v-groove, this would stop them derailing should the groove get twisted or warped....????

[Gina]

I don't think there will be much warping or twisting - I haven't detected any movement.  The type of construction should minimise this.  I'll explain what I mean when I've found the appropriate photos (or taken some more when it stops raining).

I managed to get to where I thought those plastic wheels were but they weren't there, so I don't know where they are.  OTOH I've looked through my original obsy build thread and found where I bought them.   They are nylon not acetal and 100mm OD.  Also, the rim and web are quite narrow and IMO there wouldn't really be enough material there to cut a V groove into.  Those points and the fact that I can't find them discourages me from using them   Here is the link.  So it's back to the 100mm OD acetal.

[Gina]

I think I shall do all the wheels the same - 26mm wide, 12mm deep V groove, 18mm wide, giving 4mm wide lands either side of the V.

[Gina]

For reference, here is a list of my observatory threads :-

http://stargazerslounge.com/topic/103600-ginas-observatory/
http://stargazerslounge.com/topic/116563-ginas-observatory-the-build/
http://stargazerslounge.com/topic/173015-ginas-observatory-build-abbreviated-final-design-aspects/
http://stargazerslounge.com/topic/172981-ginas-observatory-build-abbreviated-overview/
http://stargazerslounge.com/topic/172984-ginas-observatory-build-abbreviated-site-preparation/
http://stargazerslounge.com/topic/172985-ginas-observatory-build-abbreviated-main-construction/
http://stargazerslounge.com/topic/166337-ginas-observatory-roll-off-roof-automation/
http://stargazerslounge.com/topic/172972-ginas-observatory-build-abbreviated-pier-construction/
http://stargazerslounge.com/topic/185706-ginas-observatory-build-abbreviated-pier-head-adapter/
http://stargazerslounge.com/topic/197084-pier-head-modifications-for-eq8/
http://stargazerslounge.com/topic/197589-preparations-for-new-eq8-mount/
http://stargazerslounge.com/topic/197940-ideas-for-pier-extension/
http://stargazerslounge.com/topic/172986-ginas-observatory-build-abbreviated-finishing-touches-and-improvements/
 

[Gina]

I have now parted off 4 26mm long cylinders.  Next step will be to drill the 12mm holes in the middle.

[Tinker1947]

I have now parted off 4 26mm long cylinders.  Next step will be to drill the 12mm holes in the middle.

Very squarely ,,,,,,,

[Gina]

Using the lathe.  Or bench pillar drill.

[Tinker1947]

The lathe with a drill in the tailstock, the wheel tight against the chuck, would be accurate, the bench drill is close to perfect if the table is level and there is a pilot hole already made..

[Gina]

What I thought

[Gina]

Been looking around for drills and can't find a 12mm one.  Two 11mm ones and one 1/2" (12.7mm)   I think I'll run an 11mm through and bore out the extra with a boring tool (home made).  Have to say, I didn't think making my own tools would be so much fun

[Tinker1947]

Does that stuff drill ok, it don't grab it as it goes in....you should get a 12mm morse taper, start of a collection....

[Gina]

It drills perfectly well though I found sharpening the drill helped a lot   I've done two wheels now.  Put the 11mm drill through then opened it up with a boring tool.  Overdid it a bit and the wheels are a bit loose on the axle/bolt.  Probably work alright though.  Actually I think the half inch drill would probably be alright - that's not a lot of clearance.

[Tinker1947]

Arte your wheels stable at different temperature...??

[Gina]

I guess the coefficient of expansion of acetal would be higher than that of stainless steel so looseness at room temperature could turn into little clearance at sub-zero temperatures.

[Gina]

Coefficient of expansion of acetal = 4.5 X 10^-5  in imperial measures - inches and Farenheight.

In (10^-6 m/m K) ^*)  acetal is 106.5 and SS is between 10 and 17 depending on alloy. 

Think I'll stick bolt plus a wheel (or two) in the freezer and see how much the looseness disappears

[Tinker1947]

You could make some stainless steel inserts and bond them into the wheel if need be.....

[Gina]

Coefficient of friction of lubricated steel on steel = 0.16

Coefficient of friction of acetal = 0.05 (but bearing on what I don't know)

[Gina]

Just checked the wheels and bolt that I put in the freezer and the one I bored out too much is still quite loose maybe not quite so loose and the one with a half inch hole is a pretty close fit though still with clearance.

[Gina]

I have ordered a 12mm MT2 shank drill from UKTools   Cheaper via ebay than on their own web site   I have good quality drills from 1mm to 10mm in 0.5mm steps.  I also have various odd drills bigger than 10mm so it doesn't make sense to buy a 1mm to 13mm x 0.5 set.  I'll add MT shank drills as and when I want them I think.

Stormy and very wet weather is back tonight

[Gina]

I am actually using my observatory tonight!   The roof has got a bit stiff - no doubt siezed up from no use for weeks

[Tinker1947]

I though about going out, took the bins out for a look round but the flu type thing i had has nearly gone don't want it to come back need to get some woodwork done..