Spring loaded worms?

[Michele Scotti]

18 hours ago, Rusted said:

Without any end loading on the flange bearings I was able to flex the PA by a similar amount.

Can you explain what do you mean with that?

18 hours ago, Rusted said:

The most obvious problem is that the RA worm housing flexing when I manually rock the telescopes in RA.
I used 70mm square tubing with a 5mm wall thickness [from memory.]
I was able to see the flexure without needing any aids.

Can you see where the flexure is stemming from? A close-up video would be a great aid although by looking at your set-up it could be the fixings clearance for adjusting the wormgear housing. I wouldn't rule out the bearings though

The big plate looks like 10mm, the square tubing 5mm, the worm housing is possibly 8mm thick. That is enough material to make a robust system. Should be somewhere else 

 

[Rusted]

14 hours ago, Michele Scotti said:

Can you explain what do you mean with that?

Can you see where the flexure is stemming from? A close-up video would be a great aid although by looking at your set-up it could be the fixings clearance for adjusting the wormgear housing. I wouldn't rule out the bearings though

The big plate looks like 10mm, the square tubing 5mm, the worm housing is possibly 8mm thick. That is enough material to make a robust system. Should be somewhere else

I checked the free play in the PA axis using the same dial gauge set-up as the eccentricity test. The telescope was pointed to the Pole with the weights down on the north side of the pier. Despite pressing up and down on the Dec counterweights, with my hands, I could only manage a change of 0.02mm in the dial gauge reading. I considered that a trivial deflection.

I could preload the PA flange bearings but it seems unnecessary. The upper, flange bearing carries the considerable load while the lower one merely aligns the heavy 50mm shaft. The self-aligning, flange bearing's, load capacity easily dwarfs any puny loads I may apply manually or via the telescopes. The large and heavy bearing's close fit on the 50mm, stainless steel shafts is excellent.

The whole PA motor housing can be seen to physically flex in line with the worm when the telescope is used as a long lever to rock the wormwheel in RA with the clutches locked as usual. Today is misty and cloudy. So I shall attempt to video this flexure while I cannot image the sun.

The stepper motors are a close fit in their box profile housings. Which limits fixing screws to Csk heads. Countersinking the holes for the screw heads inside the narrow box sections required some ingenuity. The limited wall thickness of the box profile severely limits the choice of screw fixing size. I could wrap sections of 75mm, angle profile, around the motor boxes for increased stiffness. Then bolt these to the main supporting plates. Though the clearances are very tight.

My main worry is that motor housing flexure alters the engagement of the worm with its wheel. This should only occur during ramping up to slewing speed. However, the telescopes must constantly apply dynamic loads during guiding and under wind loading. Touching the telescopes produces severe shaking of the image at typical solar and lunar magnifications. Which is why I originally applied electric motor focusing. I must be rid of this shaking to broaden the wind conditions under which I can safely image.

 

[Rusted]

Okay. A quick video showing the general looseness of the RA wormwheel/motor housing.

Not only is there obvious end play in the worm bearings but the housing itself is flexing.

[Rusted]

And a second video from below confirms the worm bearings are not being restrained.

 

 

[Peter Drew]

Bit of work to do there I think!      🙂

[Rusted]

49 minutes ago, Peter Drew said:

Bit of work to do there I think!      🙂

Whoops! Well spotted!

I dismantled the whole drive assembly the other day and missed the washer which takes out the end shake on the worm.

[Peter Drew]

These things do happen, I once rebuilt a Velocette Venom engine and was surprised it had no compression when I tried to start it.  I suspected a valve lifter malfunction until I noticed a spare pair of pushrods I didn't have beforehand.      🙂   

[Rusted]

4 minutes ago, Peter Drew said:

These things do happen, I once rebuilt a Velocette Venom engine and was surprised it had no compression when I tried to start it. 
I suspected a valve lifter malfunction until I noticed a spare pair of pushrods I didn't have beforehand.      🙂   

Not so much "high pushrod" as no pushrods at all. 

[Michele Scotti]

Very useful vids - I see 3 things:

1) the wormgear sliding into the bearings - is that what is fixed by the missing washer?

2) the hosing movement - you describe it as flexure but it's not clear from the vid. Another video from the side would clear that. Again I'm a bit skeptical that a 5mm square tube will move much. It's maybe more likely that it's sliding/tilting due to the screw that allows the springed housing?

3) the big plate the housing is mounted on is seen deflecting  small movenet but it's there. It'd be surprise that such plate is flexing - if it's the RA shaft housing to the pier then you might have another problem to check. That should be rock solid imho as it's the fundation of the mount 

[Rusted]

Thanks and correct on all counts.

Getting the exact angle I need for the camera is quite difficult.  The wheel obscures the view from each end.
I'm using a video tripod with rise and fall head and a short zoom lens to be able to frame the view exactly.

Fitting the angle profile, on the left of the worm housing, has denied the spacer washer its former seat.
Plus the four outer retention washers are no longer functioning.
I'll be back with another video later. First I have to sort out the ridiculous end play in the worm.
Then [hopefully] the inherent flexure in the worm housing can be properly seen in isolation.

 

[Rusted]

Okay. After a whole morning of dismantling, rebuilding and fiddling I have two more videos.

I used a temporary fibre washer to take up the end play.
Just as a proof of effort expended.
I'd need the lathe to make a new stainless steel washer.
No desire to stand at the lathe at 36F with my nose dripping.

 

 

 

 

Watch later

 

 

[Horwig]

Sorry, here I go again, I'll refer you to this follow-up thread from last year:

 

lots of work done here on worm end float, play-less hinges etc etc, don't know if it is relevant to your problems...

 

Hope it helps

 

Huw

[Rusted]

7 hours ago, Horwig said:

Sorry, here I go again, I'll refer you to this follow-up thread from last year:

 

lots of work done here on worm end float, play-less hinges etc etc, don't know if it is relevant to your problems...

Hope it helps

Huw

Thank you Huw. Sadly I have no recollection of your thread. My failing memory must be even worse than I feared.
You seem to have been struggling with your Beacon Hill parts in a parallel universe to my own.
Your approach is far more sophisticated than my own. I have never tried PHD.
Only now am I considering screw adjustment of worm/wheel mesh. I usually adjust by feel alone.

Angular contact bearings, of identical dimensions o the originals, would/might reduce end play.
More importantly, without altering the original dimensions of the channel section worm "housing."
There are NO taper roller bearings available in the 12mm bore x 28mm outside dimensions. Even ignoring the width.

There is a very severe clearance constraint before the worm drive pulleys jam in the wheel teeth.
Or, the wheel rubs on the opposite end of the [channel section] worm "housing." Already much filing required.

Which means increasing overall bearing dimensions would require that they be moved outboard of the present simple channel.
Which is physically impossible within the present limits on worm shaft length. There is hardly enough room for a pulley to grip. 
Fitting outboard bearings to supplement the originals is also impossible for the same reasons given above.

I am using triple grub screws at 120° on all my timing pulleys. It was the only way of keeping them on.
I edge drilled the support metalwork to allow a long section hex key to reach the hidden grub screws.

My brass worms are presumably bonded to the steel shaft with something like Loctite. Or even shrunk on?
I could remove the worms and turn more generous shafts to fit larger, more widely separated bearings.
Possible risk of even worse eccentricity? Could I alter/spoil the metallurgy of the brass worms if I heat them?

I have searched for "flexors" but came up empty. Is this a generic term for a flat, blade spring?

[Rusted]

Some progress:

After hours of searching very unhelpful bearing websites I found some angular contact bearings in the matching size to the original deep groove.
12x28x8mm for a straight swap.

Whoever produces these bearing websites needs a course in customer satisfaction. Endlessly random size listing and filters which completely ignore entries.

Nothing in Denmark that I could find. Had to buy them from the UK. Delivery by snail mail.

https://simplybearings.co.uk/shop/p88002/Budget-7001-Single-Row-Angular-Contact-Open-Ball-Bearing-12x28x8mm/product_info.html

[Peter Drew]

There still seems to be excessive "rock" between the wormwheel teeth and the worm, as though the mesh needs adjusting, I would expect no visual movement if all was well.  One of the design shortcomings of the GEM is the relatively small area of contact support to combat the inertia imparted to the RA axis, relying on just the worm bracket and a few gear teeth.  When I built the "scrap box" mount for my 8.5" F12 refractor I adopted the polar disc modification, this gives much wider contact support, the effective bearing diameter is over 12".  My worm and wormwheel RA drive isn't on the RA shaft, a relatively small wormwheel is attached to the substantial main housing and drives the East bearing roller that co-supports the disc.  Both RA and Dec gears are permanently adjustably clutched and the telescope can be finger tipped in any direction even when driven.  Most users are surprised how easily moved and backlash free the system is, none more surprised than me!

[Horwig]

6 hours ago, Rusted said:

I have searched for "flexors" but came up empty. Is this a generic term for a flat, blade spring?

Yes, it's a strip of 0.2mm stainless steel, as long as possible, constrained by stronger strips on both sides, so it can only bend evenly with no twist along its length,

something like this in cross section:

[Rusted]

Thank you both.

I have made roller bearing, disk mounts up to 24" diameter but never motor driven. Using AWR drives I cannot manually move the mounting. Motor drive only.
Not quite the same thing, but I added a 7" [180mm] diameter, thick disk at the top of the PA to spread the loads into the Dec housing. The Tollok bush expands into it for improved stiffness.

The disk mounting has the problem of securely attaching the Dec axis housing unless the disk is made very large.

Thanks Huw. Similar arrangement to a precision clock, pendulum suspension. I'll have a dig in my scrap, phosphor bronze collection.

[Michele Scotti]

2 hours ago, Peter Drew said:

There still seems to be excessive "rock" between the wormwheel teeth and the worm, as though the mesh needs adjusting, I would expect no visual movement if all was well. 

If the camera is on a tripod on the floor what I see is that the wheel is moving away from the wormgear assembly.

I almost have the fealing that the entire RA shaft is pushed around by the reaction on the teeth. On the video from the right side you clearly see that the housing and the mounitng plate experience small deflection.

From the 'front view' video instead the deflection of the wormgear assy is more pronounced. I'm a bit baffled - would you agree with the observation?

For peace of mind I'd take a vid from the left side too and another one where you can check whether the main RA shaft and its housing are moving relatively to the main pier.

 

5 hours ago, Rusted said:

After hours of searching very unhelpful bearing websites I found some angular contact bearings in the matching size to the original deep groove.
12x28x8mm for a straight swap.

Angular bearings are a good decision - you nee to have a strategy to pre-load them though. It should be feasible with the housing you have though by adding a small plate.

[Horwig]

Here's what my Beacon Hill worm blocks look like. this is from before last year's re-build, so still has the old hinge mechanism and stacked flange bearings.

The 'U' channel has the ends chamfered back for wheel clearance, and the thickness of the end sections was cut back slightly so the plates on the end preload the bearings.

The step in the worm shaft lines up with the inner dimension of the channel section, I assume yours is the same.

With this old hinge design and the stacked pillow block bearings I was getting horrible movement of the DEC axis, work on both problems has brought it under control.

 

Huw

 

 

[Rusted]

Thank you Huw. Sorry I didn't answer yesterday. I am unwell. I'll be back.

[Horwig]

3 hours ago, Rusted said:

Thank you Huw. Sorry I didn't answer yesterday. I am unwell. I'll be back.

Sorry to hear you're not well, keep safe and warm, health comes before telescopes.

Huw

[Michele Scotti]

On 30/11/2020 at 14:44, Horwig said:

Yes, it's a strip of 0.2mm stainless steel, as long as possible, constrained by stronger strips on both sides, so it can only bend evenly with no twist along its length,

something like this in cross section:

Hi Huw, can you explain this sketch? Apologies if it's explained somehre else but couldn't find anything.

[Horwig]

Sorry Michele, my tech drawing skills are terrible, and I don't use any helpful drawing packages, just Photoshop, so here goes in 3d

Does that make any more sense?

The green is the 0.2mm strip of stainless, the blue is the part of the mount/worm block, and the brown/orange are the fixing strips.

I find this works really well, having great stiffness to sideways and twisting forces, whilst allowing a relatively good hinge angle, since the max it has to open is the tooth depth of the worm.

I first used flexors in a Clement focuser I built a few years ago:

 

 

Huw

[Rusted]

Thanks Huw.

I'm studying my options.

 

[Rusted]

Update:

Today I slid a 3' length of 50mm bore, metal pipe over the extended lower end of the PA shaft.
There was no detectable play in the PA flange bearings despite my best efforts at leverage in all directions.
Suggesting only the illusion of lateral PA movement when the 6" telescope was used as a lever in the video.

I'm still doodling potential motor/worm mounting ideas to include the clever "flexor" hinges.
I need these "hinges" to be much nearer the worm housing and further away from the motor housing.

The belt drive can easily manage the tiny movements required for the worm to maintain mesh.
New, longer belts are readily available, if needed.

The box profile, motor housing is an ideal support for the worm, for height, but only in the cosmetic sense.
The heavily cutaway, box profile seems to badly lack rigidity.
So, ideally, the worm housing should be treated as a separate, hinged unit.

Or, the hefty, stepper motor could be tightly packed around, with suitable shims.
To make the motor into a structural element of the box profile, worm support.