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  #121  
Old 15-04-2010, 03:55 PM
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kinetic (Steve)
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Quote:
Originally Posted by Spanrz View Post
My thoughts Steve, a ball roller (anti-friction bearing) to be used instead of a bush.
Or with new bushes, use Moly based grease.

Yes, I hate the sounds of metal grinding too....
Brett, yes mate, I think in hindsight the bush might have been
a bad mistake. It's easy to bore the block out to suit a ball race
but I really thought a bush would be ok at the non thrust race end.
You can see from post #70 how the cradle arrangement is.
http://www.iceinspace.com.au/forum/s...9&postcount=70

When first set up the entire carriage had zero end play(thrust) and
zero side play (bearing one end and bush other)
Now after probably a ballpark figure of only 10 complete revolutions
of the worm gear there is zero end play (thrust) but some obvious
play in the brass bush.
This will have to be re-made, no two ways about it, so I may as well
install a ball race.

Steve
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Last edited by kinetic; 16-04-2010 at 05:36 AM.
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  #122  
Old 04-09-2010, 04:15 AM
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kinetic (Steve)
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Quote:

Hopefully back in business.

Steve
An update:

Now many months on and many revolutions later of the worm gear.
Mesh is fine, tracking consistent, checking on the grease every so
often. The only thing not co operating now is the weather

I have the worm gear with index marks now so I can load PEC data
to suit which 'part of the pie' I'm using on a particular series of nights.
The PEC curve varies but only slightly. The PEC for '12 o'clock' isn't
the same as the PEC for the '6 o'clock' , as explained in a previous
post.

The Bartels software allows me to load up a custom PEC curve from
a list. Many nights over many months I have simply been generating
PEC curves and playing in Excel and other software to average and
smooth these curves. I have a pretty good indication of the accuracy
of the hob now and know that another gear (MkII) could have a lot
of things done slightly different to improve the errors I have in this set.

Steve

Last edited by kinetic; 04-09-2010 at 04:36 AM.
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  #123  
Old 28-11-2010, 05:09 PM
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kinetic (Steve)
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A bit of prep work today making a backup RA gear for the homemade
GEM.

I faced both sides for the clutch pressure plates, cut the pre-hob radius groove,
and finally bored out the centre to interference fit the RA axis.
The blank is now ready on the spindle. Next to do is the new ACME worm and hob.

This gear hopefully will try and address the main errors which have shown up
in this entire project....which are quite minimal considering how the gears
have been hobbed with a self indexing etc.

I think I can deal with both of the main PE contributors by the sequence
that I do things this time and an idea I will try with self indexing.
I will also try some mathematics this time and see if I can target a predetermined
number of teeth on the worm gear

With luck this will be the working gear (with a better PE) and the current
one will be a backup should tragedy strike

Also attached is a beautiful set of MFM hard drive heads showing a
set of 6 roller bearings (4 visible in the shot).
Nice working parts for a Crayford focuser guts

Steve
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  #124  
Old 05-12-2010, 08:44 PM
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kinetic (Steve)
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Made the hob / worm today.
I added a section to test thread cutting....PIC 1...the purpose was to
check the sharpness of my ACME tool shape before cutting the main
hob and final worm.
I'm glad I did this because I had assumed my thread cutting gears
were still set up to do an M12x1.75.
Turns out it wasn't and I luckily found this out on the test section.

Once sorted I cut the hob and worm and pic 2 shows a close up of the
final ACME thread profile. Good enough.
On to the hobbing....

Steve
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  #125  
Old 06-12-2010, 09:54 AM
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Steve,
Do you plan to do some polishing as the final stage?
A friend of mine used diamond lapping paste when modifying his EQ6 (from ebay, http://cgi.ebay.com.au/12-pcs-5gram-...item51962bab92).

The end results are fantastic in terms of PE - it was reduced from 30arcsec pp down to 7 arcsec pp, see here:
http://tech.groups.yahoo.com/group/EQMOD/message/26509
http://groups.yahoo.com/group/EQMOD/...25881/pic/list

Last edited by bojan; 06-12-2010 at 06:08 PM.
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  #126  
Old 06-12-2010, 03:12 PM
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kinetic (Steve)
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Hi B,

yes I did lap the RA worm but I didn't use carborundum (from my mirror
grinding kit days) because I didn't want grit anywhere near the workings
of my lathe.
I used cutting compound and used the worm section (not the hob).
I took a little more time to lap the RA gear, the DEC didn't get any
attention I don't think.

Post 117 shows I measured the PE at +/- 5 arc sec but I have since
found that the PE changes 'around the clock face' of the worm gear
due to the self index creep. (That's with PEC turned on BTW)
I have different PEC files I call up depending on what 'hour' of the
RA I use.

thanks for the links mate, I'll give them a look when I'm home from
work.

Steve
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  #127  
Old 12-12-2010, 07:40 PM
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kinetic (Steve)
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RA backup Gear complete

This one ended up with 323 teeth and I calculated 323!
Self indexing was helped by graduations done in the 4 jaw acting as
a rotary table.
Final depth was also as calculated...0.875mm which for an ACME
thread is pitch/ 2 and a 29 degree tool.

I made a video this time of the hob/ worm polish process.
That makes 3 successful gears from this process.

Pic 1: at half depth on the hob
Pic 2: full depth and now polishing on the worm section.
Pic 3 and 4: final product

Steve
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Click for full-size image (backup_323teeth.jpg)
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Click for full-size image (backup_323teeth2.jpg)
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Last edited by kinetic; 21-12-2010 at 08:43 PM.
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  #128  
Old 12-12-2010, 08:46 PM
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Steve, you are a legend !
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  #129  
Old 05-01-2011, 05:09 PM
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kinetic (Steve)
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Recovered the worm/hob from the lathe today and managed
to retain it's concentricity with the recovery process.
Ready to test as a matched pair now but I will wait until
near full moon so I can keep imaging with RA worm gear Mk1 until
then

Steve
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Click for full-size image (pentax 015r.jpg)
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  #130  
Old 30-01-2011, 11:48 AM
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kinetic (Steve)
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Excellent seeing and a new RA Worm Mk2 result

Last night I was able to do a very fine PEC analysis and generate
a waveform for the MK II RA worm/gear set I recently hobbed.
I had cautiously hoped the 2nd worm gear would be a slight improvement
on the PE of the MK I gear as I had done a few things different in the
machining sequences. I knew which errors were the biggest contributors
after many months of watching it and measuring MK I perform on the sky.

Also,
in a testament to just how good the seeing was last night (and hopefully
tonight), I usually can only stack about 250 from 300 frame sets.
These two results are a stack of EVERY frame in a 550 frame set for the star field
and EVERY frame in a 302 frame set for Miaplacidus/NGC2822.

Not only that....the 2822 shot has NO GUIDING and PE turned OFF
The star field shot has NO GUIDING and PEC turned ON.

Do you think I was a little bit pleased with this worm gear?

some pics of the changeover:

Pic 3: old pair on the left, new on right
Pic 4: damage I found on the cork clutch face.
Pic 5: dismantling the worm carriage to add the new worm.
Pic 6: made a new bush for the non-thrust end.
Pic 7: in mesh and testing play.
Pic 8: up and running.

Steve
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Click for full-size image (PEC_ON_19250_result_allframes_crop_qm_stshpn.jpg)
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Click for full-size image (NGC2822_result_all_frames_qm.jpg)
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Click for full-size image (changeover_under_way.jpg)
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Last edited by kinetic; 30-01-2011 at 08:29 PM.
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  #131  
Old 30-01-2011, 12:06 PM
Mighty_oz (Marcus)
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That's looking very good, u must be chipped Is this with the usual 5 sec subs or longer ?

Marcus
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  #132  
Old 30-01-2011, 08:32 PM
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kinetic (Steve)
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5 sec sets Marcus....could have easily gone longer but PE measurement
and logging needed fine resolution down to 1 sec exposures so the
night was a mixture of 1sec for PE measurement and 5 sec to try
a PEC curve in operation.

Quote:
Originally Posted by Mighty_oz View Post
That's looking very good, u must be chipped Is this with the usual 5 sec subs or longer ?

Marcus
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  #133  
Old 05-02-2011, 08:48 AM
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kinetic (Steve)
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PE measurement Gear MK II

Ok,
here are a few Excel chart results of some initial PE measurement.

I have only done a rough PEC curve and tried it just once.

I'm pretty satisfied this gear is a winner. I hope I don't chew this one out
and can, at a later stage , make a similar one from brass or steel
and duplicate the machining sequence.
This gear has so far (gone about a 1/4 of the way around the gear)
got a PE (without PEC on) of about +/- 5 pixels.
This is slightly over +/- 5 arc seconds with a conversion of 1.14 arc sec per
pixel.
Worm gear mark one had +/- 25 pixel drift (see post 117)

Thanks to Andrew (Mithrandir) and Sheeny for the tips in Excel.

Steve
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Last edited by kinetic; 05-02-2011 at 09:07 AM.
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  #134  
Old 17-04-2011, 08:57 AM
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kinetic (Steve)
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Another PE result RA Gear MKII

This is a result from last night with my cooled DSI II camera.
It represents tracking for 52 minutes on the same field at 1524mm FL.
Approx 12 cycles of the worm.
No guiding or corrections done during this 52mins.
The FOV is approx 14 arc mins x 11 arc mins.
Every frame of 500 frames was used in the stack to get the result.
Seeing was very good.

The align file was loaded into Excel and correction for sky rate error
applied using Sheeny and Mithrandir's previous suggestions.
This makes the sine wave trendline flat and shows the drift of PE
better. Green is before correction, red is after.
Just over +/- 5 pixels drift over 52mins unguided.
At 1.14 arc seconds per pixel that would be around +/-6 arc sec drift.

A happy chappy

Steve

PS:
Note the fuzzy in the neg shot....still trying to identify what it is .....
Attached Thumbnails
Click for full-size image (16apr_1_6x_result_crop_curves_x3_lapl_bmp_pos.jpg)
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Click for full-size image (16apr_1_6x_result_crop_curves_x3_lapl_bmp_neg.jpg)
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Click for full-size image (PE_RA_MkII_16Apr2011_fan5v_PWM_pelt_neg.jpg)
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Last edited by kinetic; 17-04-2011 at 01:16 PM. Reason: made chart a negative, easier to see
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  #135  
Old 27-04-2011, 08:37 PM
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Hi Steve, excellent work, just managed to go through this whole thread. You have done a terrific job in making the gears etc.. my hat goes off to you..

Where did you get the 60:1 gear reduction from? I have been trying to find something similar for my NEMA17 steppers that I use on my little star tracker I made. Also where did you source the aluminium from to make the worm wheels from?
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  #136  
Old 02-05-2011, 09:26 AM
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kinetic (Steve)
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Hi Andrew,

I just noticed your post, I've been talking to myself a bit in this thread
lately
It makes a good log of my progress if nothing else

The 60:1 gearbox is a very well built US reduction from a heavy duty
Pan-Tilt camera housing.
I have looked around for a 2nd one so I can duplicate the drive arrangement
better on the DEC axis eventually. As it happens a good friend found
me one recently so that will be the next phase.

Worm gear blanks are aluminium 'Electrical Cables buried below' marker disks.

Edit: (reading forward) Bob, Andrew, i will try and post some pics of the internals of the unit....


Steve
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Last edited by kinetic; 02-05-2011 at 12:22 PM.
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  #137  
Old 02-05-2011, 11:28 AM
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Pan/Tilt

Steve thanks for that bit of info.

I've got an old outdoor pan/tilt device that I'd been eyeing off for a while in my look at onday list. I've just pulled it to bit's for a look. The gearing is all plastic but looks well made. One beautiful bearing on the Azimuth axis. The motors are 24VAC, 7W with a nominal 3rpm output.

Bob
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  #138  
Old 02-05-2011, 12:53 PM
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Quote:
Originally Posted by hikerbob View Post
Steve thanks for that bit of info.

I've got an old outdoor pan/tilt device that I'd been eyeing off for a while in my look at onday list. I've just pulled it to bit's for a look. The gearing is all plastic but looks well made. One beautiful bearing on the Azimuth axis. The motors are 24VAC, 7W with a nominal 3rpm output.

Bob
Is it something like this?
http://www.dhgate.com/outdoor-pan-ti...2f7b153da.html

Looks interesting....
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  #139  
Old 02-05-2011, 03:52 PM
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Thanks for the info steve, much appreciated.
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  #140  
Old 02-05-2011, 06:19 PM
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Almost the same

Bojan was was similar, the alt axis looks identical but there were some differences in the moulding of the lower portion.

At a guess the one I had was an older model and I'd suspected it of being a lot more expensive than that. Thanks for the link.

Bob
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