Backlash in Crayford

[Moonshane]

I have an otherwise excellent TS Monorail focuser on my refractor but it suffers (rather unusually I think?) from a little backlash. This means that when you focus either way with the 10:1 reducer the focus shifts ever so slightly back again; you can feel this when you put your finger on the drawtube - as you release the fine focus it moves back or forward slightly depending whether in or out focusing.

I can get around this by overcompensating slightly but it's getting annoying. When the tensioning screw is completely backed off there is no backlash and the wheel turns precisely although the drawtube then has no friction. This suggests to me that it is the tension on the bar itself that is creating the backlash but I have taken it apart to no avail. One thing I did notice is that the grease around the reducer bearings is very thick and I may change this but in truth I doubt this is the problem given that there's no issue with the tensioner backed off. I have cleaned the rod and every thing is smooth apart from this backlash issue.

Any ideas please?

[Astrobits]

Try holding the knob a little while longer in case it is thick grease taking time to catch up with the metal bits. The only other thing that I can think of looking at is the tensioner screw to bar interface. ( I don't know the focusser in question but I an assuming that the tensioner screw pushes on the bar. )

Is the tensioner screw thread worn and loose allowing some slop? Just some initial thoughts.

Nigel

[Moonshane]

cheers Nigel

I'll try both later on. 

[faulksy]

is there any shims underneath the adjusting bracket not allowing the full load of the bar on the draw tube face, when you adjust the thumscrew is it central to the draw tube or does it tension on the adjuster knob.im sure a man of your caliber can sort that

[Moonshane]

cheers Mike

The design is not like a lot of other crayfords I have seen. I'll have another fiddle later.

[Moonshane]

Sorted it. I was convinced it related to the pressure on the pin and looking at it's mechanism, the direct pressure of the tension thumb was on a plastic channel. I replaced this with one created quickly out of Teflon and it's much improved. Will make a neater one in due course unless it continues to work as well as it does currently!

[faulksy]

Sorted it. I was convinced it related to the pressure on the pin and looking at it's mechanism, the direct pressure of the tension thumb was on a plastic channel. I replaced this with one created quickly out of Teflon and it's much improved. Will make a neater one in due course unless it continues to work as well as it does currently!

nice one shane. i knew you could sort it

[Astrobits]

Glad you sorted it

Nigel

[Moonshane]

It's annoying that designers of precision 'tools' when considering the construction of parts at the fulcrum of pressures don't use materials that are robust and suitable. especially when as in this case it would cost pennies at the source to make them.

[Astrobits]

There are too many things that are not designed with the user in mind.

Nigel

[nightfisher]

I am surprised that its still hard to get a really nice rack an pinion focuser, when i had the WO ZS71 i thought that would have the perfect focuser but in truth it did not meet my expectations, though it was an early model, was a nice little scope though.

Glad you sorted this little problem

[Psychobilly]

I am surprised that its still hard to get a really nice rack an pinion focuser, when i had the WO ZS71 i thought that would have the perfect focuser but in truth it did not meet my expectations, though it was an early model, was a nice little scope though.

Glad you sorted this little problem

Televue and Vixen do some nice ones...

Peter...

[Moonshane]

and Feathertouch!

to be fair, the odd skywatcher one is usable. 

[Gina]

I am surprised that its still hard to get a really nice rack an pinion focuser, when i had the WO ZS71 i thought that would have the perfect focuser but in truth it did not meet my expectations, though it was an early model, was a nice little scope though.

I am very pleased with R&P focuser on the SW Esprit 80ED Pro - nice and smooth and pricise too

[Psychobilly]

and Feathertouch!

to be fair, the odd skywatcher one is usable. 

I was going by my experiences of the OE rather than aftermarket ones...

I finally won my battle with my WO  Two  Speed Crayford so the Megrez 72 is now set up for Digiscoping  

Peter...