18 replies to this topic

[tsk1979]

I recently got a telescope with Bob's knobs installed and the classified advertisement also had it in the highlight. So I also put it as a highlight in my advertisement.

 

However, I see these are simply M3X10mm/12mm depending upon length knurled thumb screws. You get a set of 10 in 304 stainless stall, or even hard plastic or zinc ... Basically every material thumbscrews come in for 5$. Speciality hardware stores have 1$/piece and sometimes even cheaper, and even sometimes in marine grade stainless steel.

 

So I am simply wondering whats so special about 7$/piece thumb screw? Is it made of some rare metal? Vibranium? Unobtanium? Hear of a dying star?

[StephenVP]

The cost may be questionable but as far as use is concerned, I use them on my C6 so I can collimate tool free in the dark without fear of having a screwdriver or Allen wrench screech across my corrector plate. I've never had trouble using them and my scope retains collimation well. 

~Stephen

[Jehujones]

No question about the functionality, but I totally agree with the OP. Why the price?

[lphilpot]

So I am simply wondering whats so special about 7$/piece thumb screw? Is it made of some rare metal? Vibranium? Unobtanium? Hear of a dying star?

It's because the research, etc., has been done. The process has been reduced to a click or two, no searching, etc. All about convenience.

[Keith Rivich]

No question about the functionality, but I totally agree with the OP. Why the price?

Its a very small community that buys from him. If he needs 7 bucks a pop to stay in business then pay the 7 bucks and be thankful someone sticks with this very difficult business model. 

[Jehujones]

Its a very small community that buys from him. If he needs 7 bucks a pop to stay in business then pay the 7 bucks and be thankful someone sticks with this very difficult business model. 

I did 

[Steve Cox]

For a reflector I absolutely love them as they make secondary collimation and fine-tuning with an autocollimator quick and easy, without having to hold an allen wrench or screwdriver and worry about dropping it down the tube onto the primary.

 

The only time I found his screws to be a detriment was on my old C9.25.  The screws are located in a recess on that scope making them hard to grip and tighten.  I could never get the secondary satisfactorily tight and had to recollimate ever single trip to the backyard.  With the factory philips screws I was able to tighten them so that I only had to collimate every 5-10 trips to the backyard, or after a long road trip.

[maroubra_boy]

Or you can make your own capped socket head thumb screws. Nothing exotic about them. One person just found a niche market to supply them to.

You have more design flexibility making them yourself.

One aspect is convenience if you buy them readymade, another is if you are say more into scope building buying from Bob's Knobs doesn't make economic sense.

I have changed the collimation screws of my commercially made Newts & used them on the dobs I made & many other places, and made my own capped socket head thumb screws. I'm currently making the spider for a 12" scope & because I make these thumb screws I am able to design the spider hub with no restrictions.

I also round off the sharp machined tips of these screws so they do not gouge into the material that the tips push against. No gouging, no gouge for the tip to slip into & far more predictable & positive adjustment of the collimation process.

But if you have the one instrument, buying from Bob's Knobs can be simpler.

Edited by maroubra_boy, 16 June 2024 - 10:54 PM.

[tsk1979]

I think people misunderstood my point. The knobs look just like thumb screws already available on the market. They look and work just like regular thumb screws. Its not a niche astronomy only product which is cheap to make but expensive because its a rare thing used only for astronomy. Its like making M4 screws with philips head and then charging 7X because we call them Astronomy screws..

 

M3 thumb scews have already been available on the market for a long time. So are these different. If so, that justifies the price. If not, its just taking a normal M3 screw, calling it with a different name 

[dnrmilspec]

I find them a solution in search of a problem.  I have used them on SCTs but had two concerns. 

 

The first concern is that they seem less precise to me than does an Allen wrench or screwdriver.  YMMV.   I find making tiny adjustments easier with the later.  Anytime we are working around the corrector we should be careful not to touch the corrector.  We should be focused on being as precise as possible.

 

The other is simply that I find that my SCTs do not require collimation very frequently.  I might say that they rarely need it.  I guess there is no harm in Bob's Knobs, but for me, they are kinda meh...

 

I admire Bob for his enterprise and fully recognize that many people like them. 

[tturtle]

The collimation screws for SCTs going back decades vary a lot in length, diameter and thread pitch so the premium price your paying for what is essentially an off the shelf screw is because Bob has figured out the correct screw for each scope make model and year. 

[tsk1979]

The collimation screws for SCTs going back decades vary a lot in length, diameter and thread pitch so the premium price your paying for what is essentially an off the shelf screw is because Bob has figured out the correct screw for each scope make model and year. 

Okay, for obscure scopes it makes sense. But why would you need to figure something out which celestron simply puts on the information page for every scope in a neat table?

[lphilpot]

Okay, for obscure scopes it makes sense. But why would you need to figure something out which celestron simply puts on the information page for every scope in a neat table?

Because apparently more than a few people either won't or don't look. They'd rather just buy whatever has been figured out for them. I know more than a few people (not just in the context of astronomy) who will gladly pay much more for such an item than walk into a hardware store. That's not how I usually operate but if it works for them, great. I've seen astro accessories that were little more than a collection of common hardware store items selling for 10x their hardware store price. But there's no "figuring out" required, which is of value to some.

[carolinaskies]

Okay, for obscure scopes it makes sense. But why would you need to figure something out which celestron simply puts on the information page for every scope in a neat table?

Why?  Because a lot of people want the convenience of not doing the investigation, research, nor effort.  The whole ready to eat meals you buy at the grocery store are about convenience.  Bobs Knobs and other devices out there are pre-packaged solutions of convenience.  All you have to do is install them and you're done.  No removing an existing screw, driving down to the well stocked hardware store(if you still have one mind you), verifying the right type and length and buying them.  You've spent $3/gas plus likely $2.59 for a pack of 6 or .59 cents each plus 30 minutes of your time acquiring them. 

When I got into the hobby a lot of clubs still had portions of the members who constructed at least part if not all their equipment, some even grinding their primary mirror.  This was especially true with most optical companies only selling parts and only a few complete telescopes which were quite expensive as aperture increased.

Bobs Knobs is simply a niche offering from a hobbyist who saw the chance to market an inexpensive packaged solution to a problem that existed or option desired.  Note that after all these years he has no real competition because the product price is inexpensive in the hobbyist scheme.  Personally I won't install them on an SCT as I see them as unnecessary in my usage scheme.      

[CrazyPanda]

OP's post made me curious. In the past I've tried finding these knobs but didn't have luck. However I think I stumbled upon the "source" of them on McMaster-Carr. Here are some examples:

 

Bob's Knobs metric screws: http://www.bobsknobs...e61/metric.html

 

Same thing from McMaster-Carr:

 

* Bob's Knobs: M3 w/10mm diameter plastic head and stainless threads: https://www.mcmaster...d-thumb-screws/

* Bob's Knobs: M4 w/13mm diameter plastic head and stainless threads: https://www.mcmaster...d-thumb-screws/

* Bob's Knobs: M5 w/16mm diameter plastic head and stainless threads: https://www.mcmaster...d-thumb-screws/

 

Etc for M6, M7, M8...

 

The specs on McMaster and the ones on Bob's Knobs are always identical save for the length, so I wouldn't be surprised if this is his source or if he's found the same supplier that McMaster buys from. He can always make shorter lengths from longer lengths, and the longest both he and McMaster offer is 20mm.

 

So let's say I add the M3 x 12mm screws to my cart on McMaster-Carr. I get 10 for $5.93 but then McMaster charges me $10.87 in shipping (ouch) for a total of $16.80.

 

If I add the same screws from Bob's Knobs, I get 3 for $22.95 + $5 in shipping, so $27.95 total.

 

Ordering from McMaster-Carr saves me about $11, and while I technically get enough knobs for 3 dobs, there's a low chance I actually need them, so the extra 7 screws I get from McMaster-Carr are likely going to live in a drawer where their value won't be realized.

 

The value provided by Bob's Knobs is figuring out what screws you need for popular scopes. To do that yourself, you'd have to take one of your existing screws out, take it to a hardware store and use a thread checker or test some nuts to see what thread and pitch it is, then order the right screws from McMaster-Carr. In some ways, the $11 savings isn't worth the time it takes for me to do that. So the service he's giving you is that he's figured out those sizes ahead of time.

 

And note, I cannot find equivalent screws like this in local hardware stores. My local hardware stores carry these little add-on caps:

 

https://encrypted-tb...0Nn2DyalA2cG4_Q

 

They are smaller in diameter and don't always stick onto socket cap screws very well. If you want them to permanently stay on, you need to use some epoxy, which is added cost, and time.

 

So while Bob's Knobs do seem expensive, there is some value there when you look at the total cost (including time) of sourcing alternatives.

 

Also, there are some operating costs associated with a business - payment service fees, taxes, licenses, website hosting, insurance, returns, time it takes to package and ship items etc. So some of the cost of Bob's Knobs is just inherent to running a business and most certainly accounts for a big chunk of the "upcharge" on this hardware.

Edited by CrazyPanda, 18 June 2024 - 01:01 PM.

[Steve Cox]

If I were to move back to a dob and had to buy screws again I believe I'd go the McMaster-Carr route, looking for screws with rounded over tips.  One thing I remember I didn't like about the Bob's Knob screws, and was mentioned above, are the sharp ends which cut into the secondary stalk making collimation harder.  On my old dob I had to add a fender washer the same diameter of the secondary.  Having proper screws that won't cut into the back of the secondary stalk makes obtaining proper rotation and alignment of the secondary buttery smooth; Bob's Knobs didn't give me that.

[maroubra_boy]

Rounding off the tio of the screws is only part of the solution. If the body of the secondary holder is aluminium, even a rounded tip will indent the much softer aluminium face the screes push against. Not as aggressively as a sharp edge but the indentation also acts in the same way as a gouge which makes controlling collimation difficult. I put a large diameter stainless steel washer between the screw tios & the secondary holder - no gouging possible then. If the crew tips are not rounded the sharp edges will still cause damage to a stainless washer.

I also don't use black oxide steel screws if they go through an aluminium body/spider hub. Stainless is better as there is reduced galvanic reaction between these two dissimilar metals.

[kksmith]

Ease of use. Not fumbling about with a tool in close proximity to a corrector plate. I don't have them...went another route. But I do see what's nifty about them. One doesn't have to be a practitioner of machinist esoterica involving screw thread/pitch to get the right ones. Sooooo...in that aspect, knowing which SCT model you have makes it an easy purchase. 

 

Biting the hand that feeds us is a constant, no matter the endeavor. 

[Orion68]

They are ok for rough collimation but not that effective for fine collimation, at least that was my experience. I could not get small tweaks to the screw, the knob would overshoot my intended adjustment every time. I got frustrated and changed out to a button head screw that takes an Allen wrench and saw immediate improvement.

 

Some folks love em, I hated them. And yes, they are too expensive for what you get. For me, they were a complete waste of money. Of course, YMMV.