telescope focuser and pipe stress

pipe stress:

starlight focuser patent US6069754A

Well, any focuser (even starlight) can be broken if you use it beyond the payload limit, or mis-use. So don't be sold by those over-engineering marketing

broken/worn brass brake:

Inside the pinion block, there is a brass brake lever in which holds the pinion shaft. The pinion shaft of the focuser sits inside 2 u-shaped openings in the brake lever. When the brake thumb screw is tightened, pressure is applied on the entire length of the brake lever and not on just 1 spot where the thumb screw touches the pinion shaft. The problem is that the u-shaped openings of the brake lever were completely worn away in which allowed the teeth of the pinion shaft to wear a groove on the flat of the brake lever and this allowed brass shavings to get into the reduction assembly. If Starlight Instruments was contacted early on about any questions regarding the focuser, Starlight may have been able to do a repair under warranty but the damage done was so excessive that brass shavings from the brake lever was in the teeth of the rack, in the reduction assembly and the brass shavings got between the drawtube and Teflon tape and damaged the roller bearings.

Megrez broken bearings

Steel bearings scratch marks

Crayford focuser

diy:

instructable

astrofriend friction coupling repair

My theory of construction is:

extender (rail + bearing/wheel) + draw tube + push-pull tilt adjust + friction brake + eyepiece compression ring

starhunter on various types of focuser

Ccd sensor tilt test jig

鏡頭同軸度調整方法

Critical Focus Zone, focusmax goldastro new CFZ ,

wilmslowastro

focusmax:

using FocusMax formula:

As an example, the Celestron HD/RASA (F/2) manual focuser has a thread pitch of 0.75mm/rev. The EAF motorized focuser has 5760 motor steps/rev. Thus, 0.75mm/5760 = 0.13(microns) per motor step. To be in the 1.6 micron CFZ, my RASA must be within 1.6 um/0.13 um/step = +/- 6 steps.

indi

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