orion 10" newtonian focuser

[Pete Presland]

hi all

i have just upgraded to a orion 10" newtonian,and need a focuser to fit to it.i bought a beauty from moonshane but unfortunately the hole size and mounting holes are different.

the main hole size is 63.7mm in diameter.

the mounting holes are 4.5 mm in diameter.

the mounting holes are 76.5 mm apart when measured along the tube.

when measured around the tube they are 74.7 mm apart.

i think it had a crayford on it ,but i am not sure any suggestions will be gladly appreciated

thanks pete

[simon84]

Place a blank over the exising holes and cut some new ones on the other side and turn the secondary around?

[Pete Presland]

Place a blank over the exising holes and cut some new ones on the other side and turn the secondary around?[/quote

that sounds a bit daunting! how easy is it to cut

[simon84]

At the end of the day its just a steel tube, obviously massive amounts of care needed but if you removed the primary and secondary you should be ok.

Careful marking out as it needs to line up nicely with the secondary.

If you dont fancy I'm sure a local engineering firm would cut it for you if you mark it out for them.

[Peter Drew]

Would it not be possible to re-drill the mounting holes to accept the "new" focuser. If the hole in the tube is too small it should be easier to open it up with a file than to start all over again.

[Pete Presland]

this looks really close! the hole sizes are very near

2" / 1.25" Crayford focuser for Newtonian telescopes on eBay (end time 06-Jul-10 10:30:38 BST)

anbody got any experience with the focuser or supplier? astronomica uk

thanks pete

[ringz]

I replaced the original 1.25" Orion rack and pinion focuser with a new 2" crayford focuser on my 10" F4.8

The metal of the tube is very thin and is very easy to file to the new size.

The main problem is the difference in focuser travel/position. I have to use an extension tube to get eyepieces to reach focus.

Martyn.

[Moonshane]

Hi Pete

I'd try and use the focuser you bought off me because it's really a nice unit. in truth it's better than the dual speed crayford I have replaced it with!! but I do like the 10:1 fine focus.

see stage three of Astro-Baby's restoration of a newt here TAL-1 Telescope OTA Strip Down Guide

she shows whats involved in filing the hole size a little bigger. I bet you'd be OK. just make a paper template off the focuser and then mark with a felt tip or similar. then file a bit and check, file a bit and check until the focuser fits. the drill your mounting holes (that's the easy bit) and you're away. This way, it's also in the right place.

as Si says, remove the mirrors first though - again A-B's guide will help here too.

I bet you won't regret it.

[inapottingshed]

Why not just make up an adapter plate? Ask a metal shop to form a curve to suit the 10" OTA, and drill/countersink holes both sides (one to suit the OTA, other to suit the focuser) - can't imagine that costing much at all.

[Moonshane]

how obvious! you could even make one out of thin ply (painted matt black) I bet.

[Pete Presland]

thanks for all the advice,i have bit the bullet and bought a crayford that fits almost prefect!

the idea of making the adaptor was sound ,but i still did'nt fancy enlarging the drawtube hole (i know i would make a mess of it,damn my negativity )

there was a couple on astroboot as well that could be adapted,but my lack of confidence beat me in the end!