Only progress this weekend has been to lock the
worm to the 8mm worm carriage with a grub screw and
test it / lap it in.
As before I screwed the whole assembly down to the bench
and ran it on a speed controlled battery drill for about an hour.
It ran very smooth but I have a slight eccentricity in the worm
sleeve now. I think I know how to fix that (thanks Dad! )
I fitted the latest test blank assembly to my DEC axis
of the homemade GEM to see how smooth it drives
with the existing DEC stepper/ geartrain.
I made two pressure plate flanges with rebates
cut into their faces for two large cork washers to sit inside.
I used old cork placemats for the washers.
This is another great suggestion from Dave G!
The M6 pressure adjustment bolts you can see in
Pic 2 act directly on the masonite backing of the placemat
cork.
The whole setup was only temporary to get a feel for
the 'stiction' and brake effect of the pressure plates
and the ability of it to protect the worm wheel from
a bump.
The setup worked beautifully.
I am so impressed with how snug this feels and works as a
brake/clutch that I will now do a proper job of the 'temporary'
pressure plates.
Steve well done. I've been doing some more play with the remnants of by car jack thread. I used the mill to cut the slots in the hob this time, much nicer result. I've made a small gear (65 teeth I think) to drive a cheapo EQ3 lookalike which I want to put a camera on.
I picked up a gearhead motor with a nominal output of 6.7RPM at 12V which is by my calculations very close to the combo I'll need to drive the RA axis of the mount (it already has a worm gear drive which seems to be need six turns of the worm per hour).
I've also just recieved four faster gearhead motors from the US which I want to experiment with to see how much range I can get with PWM speed control.
Unfortunately my normal laptop is dead at the moment so I don't have access to software to shrink photo's etc.
I finally got the set up for the small worm gear mounted and connected to the motor. I've used some 25mm OD (19mm ID) ally tube to hold the bearings for the worm and attached it to an EQ mount which came with a Dick Smith 4" Newt. A bit of motor noise - if the rest works out Ok I'll revisit the motor mounting and add some sound deadening. I've not tried to fit thriust bearings or spring load the worm on this one, I doubt I need either for the intended use and I'm trying to keep it simple. A good learing exercise.
I've had a closer look at the thread on the worm and it is deep with quite sheer sides, not acme but it still appears to give good contact.
I've got the motor hooked to a 12V battery and am giving it a long run to see how close the rotation speed is over a period. The mount has 24 time divisions on it so I should be able to check at any time and see how well it's gone. All being well I can hang a camera off it for wide field work.
Sorry no photo's yet, I'm still trying to work my way through a warranty fix on my main laptop.
Bob
Last edited by hikerbob; 01-06-2009 at 07:32 PM.
Reason: Adding photos
I've edited my previous post and added a few photo's of the work gear and worm holder I've added to my EQ mount. Sorry about the quality of the photo's but along with the description it should give an idea what I've done there.
You can get far smoother cutting action with a spiral flute tap.
It also has a "centre" drilled in the end for centering on a live centre in your tail stock.
One thing I noticed with the normal tap is that it shudders every time the cutting edge touches the work (3 times per rev with normal taps) and in doing so could introduce minute variations that in centering because of flexure of the workpiece.
With a spiral flute tap, not only can it be centered 100% and supported by the tailstock in a live centre (thereby staying 100% true) but there is always constant contact with the cutting edges. This makes for a much more constant force thereby ensuring a smoother, more accurate cut.
I'll take a pic of my spiral flute tap and post it.
Martin
Last edited by MLyons; 04-06-2009 at 01:38 AM.
Reason: Added pics
You can get far smoother cutting action with a spiral flute tap.
It also has a "centre" drilled in the end for centering on a live centre in your tail stock.
One thing I noticed with the normal tap is that it shudders every time the cutting edge touches the work (3 times per rev with normal taps) and in doing so could introduce minute variations that in centering because of flexure of the workpiece.
With a spiral flute tap, not only can it be centered 100% and supported by the tailstock in a live centre (thereby staying 100% true) but there is always constant contact with the cutting edges. This makes for a much more constant force thereby ensuring a smoother, more accurate cut.
I'll take a pic of my spiral flute tap and post it.
Martin
Great suggestion Martin, thanks for the tip.
Might be hard to get in an ACME form though.
Because I've started making the actual worm hob on the lathe
it is perfectly concentric. But I have only ever cut parallel facets
in the hob with a dremel so far.
I might try an angled facet with the dremel to see if it chatters less.
BTW on very low speed (the same lowest speed that I turn the hob thread with), the hobbing process does chatter but only minimally.
Once the cut is almost full depth it is surrounded by the root radius
metal and chatter is almost nil.
Following the reasonable success of cutting several
gears now and fitting the best result to the DEC axis,
I was ready to start on progress on the RA gear.
Started with preparing the blank by turning it down to
the required diameter and then adding the pre-cut groove.
Also bored the centre to the size of the spindle flange
and faced two sides for clutch plates to act on.
Then turned up the worm/hobber.
Again I used M12 x 1.75 ACME profile with a 29 degree tool.
This time I chose a different approach for the worm.
Instead of the worm being a sleeve that would slide over
a 'worm carriage' I decided to make the worm and carriage
one and the same. This hopefully will eliminate the slight
eccentricity I have ended up with when I previously 'recovered'
the worm after finishing the hob processes.
I will cut the bush/ bearing shoulders and end thread on this next.
Once again I cut flutes in the hob section and put a slight
helix on these as per Martin's suggestion below.(the spiral
fluted tap).
Mounted the blank on the spindle post and wound in until contact
was made with the pre-cut groove.
This became thread depth 0.00
On the lowest speed I did the self index, again success!
I was so glad this worked because the RA I wanted to be a good
result, not just a gear with mostly a good thread and a bad part
that would be continually driven 'to the bottom' and never get used.
Then I gradually wound in 2thou cuts with cutting compound as
per previous attempts until nearing final depth of 34thou.
For the final polish I bedded it in on the section that would
be the final worm.
A few dozen rotations on full depth and it was done.
This one ended up approx 175mm dia and 317 teeth
(exactly the same as the DEC axis final working version)
Pic 1: Removed the hobber section from the worm/hobber by
turning it down to a smooth 10mm shoulder both ends of
what will end up being the worm.
Also turned a shoulder for the thrust bearing hardened washer
to rest against and also turned a 6mm end thread for the
nylock nut.
Also turned a groove for the non-thrust end bush circlip.
Pic 2: Next I made the bearing/bush blocks, again the same method
as for the DEC axis. Faced a rectangular block pre-bored to
worm shaft clearance.
Then bored them to suit the bush and thrust races.
Made one of the fixed pressure plate clutches on the weekend
for the RA axis.
This one is fixed to the RA shaft with several grub screws and has
a cork insert made from an old placemat. The same as I did with
the DEC axis. This idea, again , was from a solution suggested by
Dave G.
Pic 1 shows the clutch plate and cork insert separately.
Note the rebate the cork sits in on the pressure plate.
Pic 2 shows how it sits in this rebate.
Pic 3 shows it resting on the face of the worm gear.Cork trapped
between.
I have to make a second clutch identical to this one for
the other face now but with pressure adjustment screws.
Today I fitted the RA worm and two clutch plates to
the homemade GEM.
Top clutch is fixed to the RA shaft with grub screws and
has a cork washer sandwiched between the worm gear.
The bottom clutch plate is also fixed to the RA shaft
but has 4x5mm pressure adjustment screws acting on
another cork washer.
I must say again, as with the DEC axis,the feel of this type
of clutch working on a well balanced GEM is divine....
it slips beautifully with moderate pressure, but takes up
and drives with only finger pressure twisting on the worm.
Again, at the risk of repeating myself, this clutch assembly
will stay even if the worm gear ends up with woeful PE.
As you can see, the worm carriage is only held so far with
some G-clamps to adjust mesh via shims.
All that remains is to fit the reduction gearbox and stepper
back on and I'm in business for the accuracy test......
Pic 1: side view of the sandwiched worm gear.
Pic 2: worm carriage in mesh underneath.
Pic 3 and 4: wide shots....of the whole assembly.
Steve, great stuff. Loving it. You've got my creative mind ticking.!
Bit of a rant here, sorry , but I need to voice my opinion of a certain industry.
I've got to the point of frustration, in searching for somewhat of a Worm Setup.
I have tirelessly looked on the web and around Melbourne for someone who has knowledge of a good setup.
Tried everything from a commerical sense to a hobby sense of gears.
Tried a few local bearing joints, gave up on that one. Only 1 place had sort of what I wanted, but I knew cost was the problem.
Many many hobby shops, no good.
Tried a mob up in QLD that sells hobby stuff, they have the best worm gear setup, I've came across, but the problem is, none of their distributors here in Vic, stocks any of their parts. They have basic pictures of what it would look like, but not spending $$ until I can see what it's going to do. I have to order it first (to see it), just to hope that it will do what I want it to do.
I wanted to keep costs (as you do) low, but it's the functionality of the setup, is what counts.
I haven't tried a proper gear supplier yet (ronson), as I know cost would be into oblivion, last resort.
So, in my midst, my thoughts are Australian industries don't cater for us Astronomers. Because, we are (in their eyes) a minority. That frustrates me. I had this feeling 20 odd years ago, but thought 2009 would have produced better results.
It's getting to the point, like your self Steve, to make your own.
Or the alternative, is the wife is organising a trip back to the USA (her home), and I know I could probably find 6 suppliers of this type of setup, in NY, all of which have stock and a better price than we can do in Aus.
That's sad. Probably 4 of them closed by now due to the global slowdown...figures. But I know what I want, I know someone makes it, but it's finding that person.
It's very frustrating to talk to a person in the know, who basically says "not a chance mate, you wont get that low" and they look at you stupid as if you are trying to re-invent the wheel. It's not like I'm asking for 10,000:1, just what ever I can get, which looks like 360 teeth.
I'm even up for making it myself, but the process with a lathe, is a little beyond me. (Haven't used a lathe for a very long time)
It's a gear with 360 teeth on it. I think it's around the 6" in Diameter, but that doesn't phase me. Everyone (retailers) think size is an issue, I said, bigger is better......Yeah I suppose what women want to hey...!
Bigger = better reduction values, but not too big.
Other than that, spare parts from a scope mount manufacturer?
Can anyone else shed some light on why it's so hard to even find a good worm setup from a local supplier?
Yep, as you mention, Byers in USA and others similar, are probably
the only source of very accurate worm /worm gear matched sets.
I'm certainly no expert to comment about how good they are, maybe
someone more experienced in that can chime in.
I'm hoping that this method can, at the very least, churn out
a gear with minimal and manageable PE.
I'm definately not an expert on a lathe, I can tell you that.
I am, however, a competent DIYer and it's not all that technical.
The pioneers like Jim Sapp and Dave G etc who take the time to
write up their engineering marvels help people like me no end!
You mention a dead end in Oz for manufacturers or suppliers.
I can suggest one avenue....I know some VERY talented
people dabble in miniature steam trains etc and they nearly always
have lathes and/or mills.
If you took the time to seek out one of these groups I bet you could
mention it to them...point them to the relevant websites and maybe
politely ask them to make you a gear for a fee.
PS: one alternative to worm/worm gearing is toothed belts.
Theo (Gama) kindly posted an example earlier in this thread: http://www.observatoryscope.com/prot...operation.html
There are suppliers in Australia for that stuff....one source
for example of a smaller set is RC car racing.
Steve
Quote:
Originally Posted by Spanrz
I've got to the point of frustration, in searching for somewhat of a Worm Setup.
I have tirelessly looked on the web and around Melbourne for someone who has knowledge of a good setup.
Can anyone else shed some light on why it's so hard to even find a good worm setup from a local supplier?
Fitted with some slight modifications to the angle iron holding
the old drive gearbox.
I have both lateral adjustment and mesh adjustment like the DEC
axis.
It feels so snug and clutches beautifully!
Now to add the drive gearbox and stepper...
Steve
PS: this hobby can be so cruel.....2 days with the scope out of
action due to motor/gear changeover....2 nights of 3 degree overnight
lows....seeing excellent....jetstream ideal!!!!!!!!!!!!!
PPS: make that 3 nights!!!!!!
Last edited by kinetic; 08-07-2009 at 06:16 PM.
Reason: PS
Brett if you are trying to buy ready made worm and gear you could try a bearing supplier. I checked into it some time back and was somewhat dismayed by the pricing (from memory it was looking like about the $400 for a set - one worm and one gear). I did not do a lot of investigation so I don't know just how good they are for our purposes.
Hobby Parts at Mansfield (they do mail order) also supply some. http://www.hobbyparts.com.au/ Again I don't know how suitable the gears are for driving a telescope. I have purchased via the web and the delivery turned up the next day which was impressive.
Bob,
yeah that's the website I got on to. After days of frustration looking, hehe.
I have tried about 20 suppliers around Melbourne, other than actual gear manufacturers (last resort).
Every supplier says the same thing "Sorry can't help - Have no concept why you would want such a reduction - No idea mate, we don't deal in that - Sorry mate, don't know who can supply such a thing"
No one wants to help or understand what I'm asking for.
I have tried about 10 odd hobby shops, all have spur gears with a lot of backlash and bugger all reduction. Most don't even stock a worm.
However, I found 2 places that had somehwat of a chance.
The local bearing shop had a supplier called "Naismith" that made a gearbox with near zerobacklash called "Zeromax".
However, functionality was looking good until it required a minimum of 140 RPM's on the input, which is sort of pointless. It needed that speed for oil splashing. And the cost for the functionality, was basically "Astronomical" , excuse the pun
The other, sort of success (if you call it that), is JAYCAR.
They have some gear sets there, but it's a case of, "Look and laugh".
They are plastic and very very light duty - for toys.
Some DC electric motors have a gearhead on them, however, lots of backlash, which was the last of the "last resorts".
Now, with that HobbyParts website, no one locally stocks anything.
Which is disappointing. Not so much what I was requesting for, but abolsutely nothing was stocked, yet they call themselves a "distributor".
I might as well order it online and get it myself. Pointless for the middle man.
I found a gear with 360 teeth on it, I have emailed them about it, but no repsonse.
It was about $200 for that gear and another $90 odd bucks for the actual worm gear.
I was actually after a Duplex Worm set, as both gears mesh / conform to each other and backlash (IMHO) is reduced to very low levels.
But this gear set is close to a duplex.
They key is, I want to see it in the flesh, before I purchase. I want to know it's going to work, but business doesn't work that way.
Oh well, they miss out on a sale.
I'm still searching all alternatives, even from my work.
Brett.
Brett Hoby Parts did have some worms on display last time I was in but I'm pretty certain that they don't have the gears in stock. Minature Bearings who I think supply that stuff to them are in the same building but I don't think that they do retail (and both are a long way from you).
I've seen printed catalog details on worm gears at Bsc http://www.bsc.com.au/html-bsc05/indexBSC.htm which they can get in. I think that had to come from overseas but they can get worm gears, from memory the multiple lead gears available were low ratio. I could not find anything in the online catalog.
I've taken a break from my hobbing attempts for a while as I do some other stuff but if I don't decide to buy an EQ6 and continue building myself I suspect that's the way to go. Hobbing the gear seems to be the easy bit, getting the rest of it machined properly has caused more trouble.
Bob,
I finally got a response from the HobbyStore.
This is so far the best concept of a worm gear I have found. (out of about 30-40 designs)
It's the cheapest version of a metal worm gear set that I could find, that is relatively sized to suit the scope.
The gear is around $200 inc gst and the worm is around $60 I think.
My ideal price range for the set would be around $100-$150, but the gear set went up about 25-30% after June 30th.
(and they call this a recession where prices should come down somewhat???)
The other ones I have found, were cheap and plastic (...pffft)
But I suppose I can't complain, as I haven't yet hit the costs on astrophotograhy........Many thousands to go....Hahaha.
Oh the joys (and expense) of a hobby.
EDIT:
I'd love to make one, I have the tools at work, but I don't think I'll have the permission to use them.
Which is the reason I have gone down the road of "purchase".
, but I need to voice my opinion of a certain industry.
And now fitted properly to the RA axis:
, excuse the pun 
