Dual Speed Focuser

[hornedreaper33]

Hey all,

 

Last Friday afternoon at work I turned myself a larger diameter (57mm) focus knob that clamps onto the existing focus shaft on my C8 SCT with a grub screw. It was a great success. I found myself looking at it over the weekend thinking about making myself a dual speed focus control. Has anyone on here tried to replicate something like the Starlight Instruments Feathertouch?

I have been lead to believe they use planetary balls rather than gears to reduce backlash. I have found some small planetary gearsets which will do the job but has anyone seen a supplier of planetary ball sets? Another problem with the gears is that I can only get 4:1 in 35mm diameter and 6:1 in 57mm diameter. I guess I could have two sets in series but that would increase the backlash (insert other problems I have yet to think of).

Anywho, if there are any people out there who have experience in DIY'ing one of these, I would appreciate the input.

 

Clear skies.

[Chriske]

I use dual speed knobs in almost all my scopes.
I buy these units in US, costs about 10$.
And no there's no backlash at all in these units.
Need to look it up, forgot where I bought them.

[hornedreaper33]

Hey @Chriske, thanks for the reply. If you could get a link for me please, that would be awesome. I have found these guys: 

http://www.orenelliottproducts.com/purchase-planetary-reduction-drive

While they appear to be higher quality and available in 10:1, they are a bit more expensive.

[Chriske]

Hey,

You beat me to it... These are the ones I was referring to.
The one I always use BD601 only cost a bit more indeed then the last time I bought them(years ago). That is if you buy them 5 at once (12$). Years ago they only cost 10$ a piece, I'm a bit surprised price got up that much.
They work very well BUT! You need to take them apart completely, take out the thick grease and reassemble them adding a bit of light lubricant. + release a bit of the pressure of the little lips that hold these units together.

The BD601 units are stamped versions, so not the same quality as the machined versions. But again modifying the BD series a bit and they work just as perfect I suppose. I always bought them by the dozen or so because we needed these for our telescope-making-course.
If you buy the BD601 let me know, I have some pictures how to take them apart and reassemble again. Reassembling is done with a bit of 'fingerspitzengefühl'. You should not press to hard on the assembly-lips to close the unit again. There are dozens and dozens in use in our telescopes at our observatory, they work just fine.

One more thing : If you need both speeds 1:1 and also 6:1 you should buy the BD601 unit.
The BD602 has ONLY the 6:1 reduction, there's no flange to attach the 1:1 knob.

Never tried the machined version myself, maybe they're far better. If you buy that one, please let me know, maybe I'll try that one also.

Good luck.
Chris

[Chriske]

This a drawing I made showing the completed unit from different angels. The bleu parts I do print these. Years ago when I did not had that 3D-printer yet we use to make them out of resin.
If you decide to use these BD601 units and you have printer, let me know, I'll send you the STL files.
The large knob is the 1:1 and the smaller one is the 6:1
Almost forgot, to fasten the large knob you need two M2 screws(they're not included)

[Chriske]

Mounted on my printed telescope.

[Gina]

I remember those slo-mo drives for decades back when I was playing with radios, for tuning drives.

[hornedreaper33]

@Gina, my searches lead me to believe that's exactly what they're for. God bless the radio hobbyists. 

@Chriske, I have seen those images popping up on Google. Thank you so much for sharing. I think I was hung up on the fact that people said they were getting the parts for a lot cheaper. I wonder if this is what Starlight Instruments are using or if they are making their own? Either way I think I shall be ordering soon and get myself a dual speed focus knob for a fraction of the price of the Feathertouch. I may even push the boat out and get it anodised ? 

[Chriske]

Feathertouch and a few other brands are ridiculously expensive.
That's the reason why we started making our own focusers with the feel of 'butterly smootness' as they like to call it.
Reminds me btw just a few years ago one open door in our observatory. A few weeks before open door a friend just bought himself a Feathertouch and came to visit our part of the OD. He started to smile when he saw our printed focusers (we were demonstrating) with that BD601 unit integrated. He took it in his hand and started focusing, just to feel if it worked smooth or not. Immediately his smile disappeared asking us : Why didn't I know you made these perfect focusers..? I paid about 250€ for that focuser. When I told hem we only spent a fraction of what he paid, he was not happy at all.

I do understand why people buy such expensive focusers. Most of us only buy(or build) one maybe two telescopes. But at the rate I build these scopes, my wife would not be happy if I would buy another Feathertouch or other expensive focuser again...

[hornedreaper33]

I've ordered the stamped 6:1. The shipping from Oren Elliot was ridiculous. What is your preferred interface between the focus shaft/screw on the OTA and the focuser assembly?

Edited February 12, 2019 by hornedreaper33

[Chriske]

I'm  afraid I do not understand what you're trying to say.

[hornedreaper33]

I was having trouble following it while I was typing haha. I'll try again, sorry. How does your DIY focuser attach to the actual focus assembly on the telescope? From this view it looks like there isn't much room to get an allen key in, to tighten a grub screw.

For reference, when I pull the rubber knob off my C8 SCT, there is a 13mm (ish) diameter shaft.

Edited February 12, 2019 by hornedreaper33

[Paul73]

Some great work there. For the rest of us, who don’t have the requisite skills, there are alternatives to Feathertouch products. I consider the Moonlite unit on the side of my Dob to be really pretty good. But, I can’t help thinking that I could make some improvements ??.

 

[Chriske]

Ok now I get it...
I'll disassemble my focuser tomorrow morning and post some pictures while reassembling it. It's almost bedtime here...
I can already say this :
The hole in the BD601 unit is 1/4" sadly enough(we're imperial) so in my case I need a very thin and small shim of copper to compensate for my 6 mm rod.
You'll need a ring to elevate the BD601 unit to overcome the height of that 13mm shaft. You must glue (or screw) that ring onto the the back of the scope. That ring should sit around that shaft.
I hope you're a handy man..?

 

[John]

2 hours ago, Paul73 said:

Some great work there. For the rest of us, who don’t have the requisite skills, there are alternatives to Feathertouch products. I consider the Moonlite unit on the side of my Dob to be really pretty good. But, I can’t help thinking that I could make some improvements ??.

 

I like the Moonlite focusers (I have 3 of them currently) but I now have a Feathertouch on my 130mm triplet and thats in another league again to be fair to it. The engineering and design quality is really superb on the FT. I can see why there is a cost associated with this sort of quality.

 

 

[Chriske]

Hi me again, and  as promised a few pictures of a another Crayford I just assembled with a BD601 unit inside.
If not clear please ask...

[hornedreaper33]

@Chriske, Thank you so much for the images. Unfortunately the C8 is very different and will require an adaptor to take it from the 0.5" focus shaft on the OTA to the 0.25" hole in the speed reducer. No matter, we have a lathe at work, I just wanted to see how you did it. 

I will watch the installation video from the Feathertouch website and see how they did it.

@John, I appreciate they work very well but $350 is a bit steep. The reducer has cost $40 when all was said and done with shipping.

[Chriske]

You do have a lathe, so it should be 'piece of cake' to integrate that BD601 reduction in your system.
There's one decision you have to make, how to attach that device onto your scope. I'd go for drilling two tiny holes in the back of your scope and use M3 bolts. There's also the possibility of gluing that lower ring.

[hornedreaper33]

There is a nice anodise orange plate held in by three M3 CSK screws that holds the bearing assembly in on the stock focus assembly. I'll just turn the body of my dual speed focuser to make use of what's already there ?

[Chriske]

These units don't look very professional, I know. But when 'tuned' there's as good as any expensive dual speed focuser.
I've don this dozens of times.

When it arrive ,see how it performs. It probably will run very difficult(due to the thick grease inside).
If so, let me know, and I'll post some additional pictures how to proceed to make these work with 'butterly smoothness'.

[JOC]

I reckon the OP has a version of my own turned knob!!

[Fraunhoffer]

On ‎13‎/‎02‎/‎2019 at 21:29, hornedreaper33 said:

There is a nice anodise orange plate held in by three M3 CSK screws that holds the bearing assembly in on the stock focus assembly. I'll just turn the body of my dual speed focuser to make use of what's already there ?

Can I check my understanding here - the flanges on the gear drive needs to be attached to the scope body in some way (e.g could adapt the orange ring / or make something similar)

thanks

 

[hornedreaper33]

Correct @Fraunhoffer. My plan is to make a big top hat shaped piece that will bolt on in the same place as the stock focus assembly. The speed reducer is in the post and I'm going away for 10 days but as soon as it's made i'll post pictures.

[Fraunhoffer]

19 hours ago, hornedreaper33 said:

Correct @Fraunhoffer. My plan is to make a big top hat shaped piece that will bolt on in the same place as the stock focus assembly. The speed reducer is in the post and I'm going away for 10 days but as soon as it's made i'll post pictures.

@hornedreaper33 Ah ok I think I get it. So pull the rubber knob off and undo the 3 screws.... screw top hat thingy in place and attach slow mo to the original shaft (minus rubber knob), and it is also attached to the top hat.
What happens exactly when the 3 CSK screws are undone and the orange round plate removed. Is there a risk of anything dropping out (before I have a peek) ?
Visions of springs and ball bearings dropping on the living room carpet....

Edited February 16, 2019 by Fraunhoffer

[Chriske]

Do not forget to order M2 bolts/screws...