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Evan
12-10-2008, 05:51 AM
I made a worm and wheel today for my telescope equatorial mount. I calculated that with the recent addition of a new gear ratio that if I change the wheel gear to 280 teeth it is within .01 percent of being able to run directly from a 60 hz step rate on the stepper drive. This would work out nicely with the crystal controlled 60 hz inverter I built to run the double arm drive and is close enough that I can bend the crystal frequency with a variable cap for fine control.

The worm gear threads were also CNC milled for maximum accuracy. The wheel teeth are at the correct helix angle even though it is a slope of only 1/285. The thread form is basically stub acme, 14tpi. It doesn't matter as they carry almost no load and run at only 1 RPD ( D as in Day). What does matter is periodic error and smoothness. The worm has been polished with a buffer.

As shown I made the cutters from 1040 carbon steel heat treated and quenched.

http://metalshopborealis.ca/pics5/ww4.jpg

http://metalshopborealis.ca/pics5/ww1.jpg

http://metalshopborealis.ca/pics5/ww2.jpg

http://metalshopborealis.ca/pics5/ww3.jpg

Your Old Dog
12-10-2008, 06:23 AM
Nice job Evan. Hope you'll show us your project when it's finished. If I had your ability I'd never sleep as I have a head full of projects I'd like to do !

torker
12-10-2008, 08:07 AM
Nice job Evan. Hope you'll show us your project when it's finished. If I had your ability I'd never sleep as I have a head full of projects I'd like to do !
Evan doesn't sleep.
Janet said he tried it once but it just made him cranky.
Nice work Evan!

Evan
12-10-2008, 09:33 AM
Evan doesn't sleep.



Look who's talking. What are you doing up at 5:00 am? :D

Sleep is highly overrated. I get by on a few hours per day.

Don't be so quick to compliment my work. It hasn't been tested yet. The proof will be in how well the telescope tracks. That won't be tried for a week or two, full moon and weather permitting.

This is what happens when you try to take night sky pictures with a full moon.

http://metalshopborealis.ca/pics/orion.jpg

aostling
12-10-2008, 07:19 PM
The thread form is basically stub acme, 14tpi. It doesn't matter as they carry almost no load

Evan,

This is really beautiful work, machining to instrument-grade precision.

You have shown how your equatorial drive is in almost perfect balance, so that (as you say) the worm set is virtually unloaded. Which means that backlash, if any, could be a problem. Is the mechanism adjustable for zero backlash?

John Stevenson
12-10-2008, 07:42 PM
What about cutting a hob to match the worm then free hob the worm wheel to get an enveloping worm instead of point contact.

Just a query and not a critism.

.

Evan
12-10-2008, 07:52 PM
Allan,

I have recently made various modifications to the drive system to make it suitable for astrophotography and removing backlash is one. It isn't that important though since it is easy to adjust the weight so there is a slight bias to one side that takes up the lash.

John,

I just recut the worm as an enveloping worm. I'm trying to figure out a way to make Mach III work as if it has full 3D interpolation. I'm going to have to write a small program to simulate it. The gear is large enough that it has about six teeth in mesh even though the worm isn't enveloping but an enveloping worm will spread out the contact area over more teeth making a better average which reduces periodic error. I am also going to try making a large diameter plastic wheel from Lexan since the larger the wheel the smaller the angular displacement caused by any periodic error.

John Stevenson
12-10-2008, 08:01 PM
John,

I'm trying to figure out a way to make Mach III work as if it has full 3D interpolation.
?? Articulate :D

Edit,
No don't bother I realise what you mean, I meant to say hob the wheel to get the curved tooth.

Forrest Addy
12-10-2008, 08:01 PM
So what happens if you get to tooto 278 and have to dexcde whether to cut one skinny one or two fat ones?

Come to think of it, if your movement needs less than a complete rev you can cut the sector you need to any number of teeht you want even fractional teeth. So you can get an accurate Sideral movement without even the 0.01% error you have with 280 teeth. That is 280.028 teeth (or 179.972, whichever) but just for a sector. You can make the sector into a full circle so long as you dom't pass the bogus tooth space into mesh with the worm.

John Stevenson
12-10-2008, 08:16 PM
So what happens if you get to tooto 278 and have to dexcde whether to cut one skinny one or two fat ones?

Come to think of it, if your movement needs less than a complete rev you can cut the sector you need to any number of teeht you want even fractional teeth. So you can get an accurate Sideral movement without even the 0.01% error you have with 280 teeth. That is 280.028 teeth (or 179.972, whichever) but just for a sector. You can make the sector into a full circle so long as you dom't pass the bogus tooth space into mesh with the worm.

Or cut a 70,007 tooth wheel and use a 250 start worm :D

.

Smokedaddy
12-10-2008, 08:20 PM
What does matter is periodic error and smoothness.

As usual Evan, very nice work and thanks for the pictures. Sure wish I had the skill, ability to try this myself. What do you "think" the PEM will be? I have a Parallax HD200C and the periodic error is ± 2 arcsec. With some work and using PemPro I can get these values down to ± 1.0 arcsec.

Regards,
-SD:

Evan
12-10-2008, 10:03 PM
I have no idea what the error may be but I will find out. I will probably want to map the leadscrew on the mill and make some more parts. I have been playing around with thread milling today and it sure is slick. Beats the heck out of the lathe for the larger diameters and the really coarse threads.

Astronowanabe
12-11-2008, 01:52 AM
so the question is still why not hob it?
even with the correct helix angle the enmeshed surface area will be less

did the depth of the cutter across the face of the gear follow the arc of the worm or was it constant depth?

Evan
12-11-2008, 02:10 AM
Constant depth. To change that is trivial if I wish. It really doesn't make a difference as the loading is tiny. There is no acceleration and the worst load it will see is when there is a wind or the scope is bumped when tracking. The system is clutched with a slip clutch that uses a teflon clutch plate and that provides really nice movement as there is no stick/slip. It also prevents any large momentary "break loose" forces being imposed on the gearing.

I will be experimenting with various arrangements and materials. This entire telescope was/is highly experimental. Another item in the program is to install a secondary focuser that can be selected by rotating the secondary mirror mount. Because of the way I have the secondary mounted it is as secure as if it were on a solid metal plate.

The metal bands are Starret .015 shim stock sandblasted and blued and are under high tension making the entire assembly really rigid. It may look like it blocks a lot of light until you look straight down the barrel. It only leaves slight diffraction spikes on bright stars.

http://metalshopborealis.ca/pics5/tscopea.jpg

http://metalshopborealis.ca/pics5/tscopeb.jpg

Astronowanabe
12-11-2008, 02:41 AM
loading was not my concern,
my belief is that maximizing contact will minimize periodic error and reduce any higher frequency roughness.
lapping the pair together does not seem like a bad idea.
(not that I have made mine yet).
and yes that is a nice scope I will have to try to get up to the Mt K... starparty and see it unless you brave the border and come down to OSP.

Evan
12-11-2008, 03:06 AM
I can't get in to the US at present as I don't have a US passport and it is too much expense and trouble to get one. I will most likely be at Mt. Kobau next year so perhaps I will see you there.

I am experimenting with different ways to make these parts simply because I can. I do run the parts together after making them to "break them in".

gmatov
12-11-2008, 03:14 AM
I have little to add except that is very nice work.

On the other Forum I asked "or should I ask Evan", and one reply was "Yes you should."

Question for you, Evan. 5 year old. Want to get a telescope. Have the option of a National Geographic branded at an off price store, 80 bucks, and this one at Sam's Club.

http://www.samsclub.com/shopping/navigate.do?dest=5&item=407870

It is cheap, but bear in mind it is for a 5 year old, well, soon to be 6.

I realize it is not a true astrological instrument.

The boy is more into paleontology than astrology, anyway. LOVES dinosaurs, as I suppose they all do.

Could you see Venus, Jupiter and the Moon in near alignment last weekend? Sky was overcast where I am. Have to wait till 2052, I guess.

Cheers,

George

Astronowanabe
12-11-2008, 04:03 AM
I have little to add except that is very nice work.

On the other Forum I asked "or should I ask Evan", and one reply was "Yes you should."

Question for you, Evan. 5 year old. Want to get a telescope. Have the option of a National Geographic branded at an off price store, 80 bucks, and this one at Sam's Club.

http://www.samsclub.com/shopping/navigate.do?dest=5&item=407870

It is cheap, but bear in mind it is for a 5 year old, well, soon to be 6.

I realize it is not a true astrological instrument.

The boy is more into paleontology than astrology, anyway. LOVES dinosaurs, as I suppose they all do.

Could you see Venus, Jupiter and the Moon in near alignment last weekend? Sky was overcast where I am. Have to wait till 2052, I guess.

Cheers,

George


around here five year olds get these

http://ix.cs.uoregon.edu/~tomc/images/ocular_mounted.jpg
robust, closed, no loose parts , erect image, light ,sized for small hands.
they come in pairs so there is one for a buddy as well.

they also work well without the mount when exploring during the day etc

cheap too. discarded binoculars, some all-thread and nuts and a bit of lathe work on scrap to the make the focusing barrel fit

Your Old Dog
12-11-2008, 06:47 AM
Evan, the conversation is a bit over my head but let me ask this. Would a 1 rpm synchronous motor about the physical size of a womans fist be of any use to you with this project? I have one that was once used by my former employer to turn a shaft with cams on it that triggered micro-switches. It's built rather robust and nothing whimpy about it.

Evan
12-11-2008, 08:07 AM
YOD, thanks for the offer. A 1 rpm motor is ideal for building a very simple tracking mount like this one:

http://metalshopborealis.ca/pics5/mount1.jpg

I already have a large stash of such motors and don't really need another.

George,

First and foremost, it's ASTRONOMY, not astrology. The former is a science and the other is nonsense. The telescope you linked to looks like fun to me. Be aware that the GoTo function isn't entirely automatic. It requires a fairly simple initial setup to use that function. Meade makes decent telescopes and the option to take images with a web cam is a nice extra.

Realize that with a small telescope you just aren't going to see the sort of things that the Hubble does. You also won't see the things that I take pictures of as they require lengthy time exposures to gather enough light to make them visible. There is still plenty to look at and it helps to have an organized plan in advance so you can set some achievable observing goals. Just knowing what is in the sky and what isn't visible helps to avoid disappointment.

I use a freeware program to plan my observing called Stellarium which is an excellent piece of software. It presents the night sky the way it will look to the unaided eye and then allows you to easily zoom in to see what is there if you have a telescope. It also helps to keep up interest when the weather doesn't cooperate and gives something to do planning the next observing session.

http://www.stellarium.org/


As for the conjunction, I did glimpse it but it was so low in the sky at this latitude I didn't pay much attention. I did get a rather rare picture of Venus, Jupiter and Mars seen in 1996 through a veil of noctilucent clouds which are themselves a rare phenomena.

http://metalshopborealis.ca/pics5/trip.jpg


BTW, that little scope with the web cam could possibly take pictures like this: This was taken in two frames with a webcam attached to a similar earlier model of Meade telescope.

http://metalshopborealis.ca/pics5/moon_comp1.jpg

Ken_Shea
12-11-2008, 09:43 AM
I can't get in to the US at present as I don't have a US passport

Evan, I was not aware of that, when did this start?

Been to Canada on several occasions and did not need a passport but that was years ago.


BTW, impressive stuff again Evan, over my head as well but is still very interesting to see.

Evan
12-11-2008, 10:24 AM
The passport issue has come up several times. The US requires that all US citizens (I am dual citizen) MUST present a US passport now to reenter the US. It must be one of the new biometric passports. To get one I have to go in person to the Vancouver consulate and fill out the forms and present my finger in order that they may take a print for the passport.

This poses several issues. It's a 1200 km drive round trip. I can't drive long distances myself anymore because of the danger of falling asleep at the wheel is extreme. It would have to be a two day excursion so it would cost hundreds just to apply for a new passport and would eat two days of my wife's vacation time.

I don't have a problem with the finger part, I can even email it to them.


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Ken_Shea
12-11-2008, 10:48 AM
Evan,
LOL - know what you mean !

Here in the US you can email no problem, it's getting them answered that never happens.

jkilroy
12-11-2008, 11:58 AM
"First and foremost, it's ASTRONOMY, not astrology. The former is a science and the other is nonsense."

I was pretty sure someone was going to catch that, needed a good laugh.

Evan
12-11-2008, 12:07 PM
I couldn't miss it. BTW, the Zodiac belongs to astronomers. We have it in the right place in the sky. Astrologers are using positions for it that are 2000 years out of date. They don't like to deal with little complications that some people's astrological sign will change during their life due to planetary precession or that two people born in different centuries on the same date may have different birth signs.

jkilroy
12-11-2008, 06:11 PM
Oh I can't wait to spring that little number on my fern feeling pot head friends back in San Francisco on my next visit. :D

derekm
12-11-2008, 06:57 PM
The passport issue has come up several times. The US requires that all US citizens (I am dual citizen) MUST present a US passport now to reenter the US. It must be one of the new biometric passports. To get one I have to go in person to the Vancouver consulate and fill out the forms and present my finger in order that they may take a print for the passport.

This poses several issues. It's a 1200 km drive round trip. I can't drive long distances myself anymore because of the danger of falling asleep at the wheel is extreme. It would have to be a two day excursion so it would cost hundreds just to apply for a new passport and would eat two days of my wife's vacation time.

I don't have a problem with the finger part, I can even email it to them.

And I believe Dual citzens need a U.S. passport to leave the U.S. so make sure it doesnt run out... As happened to a friend of ours he couldnt get back out of the U.S. on his British passport...

Seems strange to us in the UK as our government doesnt yet have the power to stop its citizens from leaving unlike l the U.S...

gmatov
12-12-2008, 12:40 AM
Astrono,

My kids already have pairs of them. Known as binoculars where I live. Still worry that they will try to look at the Sun with them.

Evan,

That embarrasses the hell out of me. I know better. What made me type astrology, I don't know. I heckle my cousin for her belief in the daily horoscope.

Thanks for the words of praise, I guess, for such a simple instrument, knowing that it is for a 5 (near 6 ) year old, and his younger brother.

I know this isn't the Hubbel. Hopefully, the lenses and mirrors are ground properly in this one.

I wouldn't assume you could just plunk it in the drive and it know exactly where it is in relation to the Earth or the Universe.

I would like for them to have an interest in the Sciences. Whether there WILL be other work for them that can pay a decent living when they become adults, I have little hope.

Regardless a scientific future or not, I think kids should be exposed to as much as possible in the formative years. One never knows what their final passion will be.

Regardless, again, forgive my use of that word, I wish I were capable of the work you have displayed. I am not, but can appreciate it when I see it. I haven't the passion for it.

Hell of it, too, is that for a 5 year old, beddy-bye is about 8:30. Summer it is to early to be dark, Winter, it is too cold to be out. Maybe Mom and Dad will let them stay up long enough to study the stars. They're worth it to me to buy it anyhow.

Cheers,

George

Evan
12-12-2008, 03:02 AM
I did some more experimenting with the worm gear. This time I tried something a bit different by using the wheel gear to hob the worm. The worm is from PTFE and I cut it fairly close on the mill and then set it up in a jig on the lathe. The worm was run against the edge of the wheel teeth which nicely shaved it down until a very good enveloping fit was obtained. It then stopped cutting which is a good sign that it fits the same all the way around.

http://metalshopborealis.ca/pics5/worm5.jpg

Tommorrow I am going to do the same thing but using Teflon LF filled PTFE. That should be interesting because the filler is a ceramic powder and will actually polish up a metal gear it runs against.

lazlo
12-12-2008, 01:17 PM
And I believe Dual citzens need a U.S. passport to leave the U.S. so make sure it doesnt run out... As happened to a friend of ours he couldnt get back out of the U.S. on his British passport...

The Department of Homeland Security has been steadily increasing the requirements for US Citizens to enter and exit the country via the "Western Hemisphere Travel Initiative." It used to be that a US citizen could go to Mexico, Canada and the Caribbean with just a driver's license. But now you need a passport for those countries if you travel by air or boat -- when we went to Antigua this Summer, we needed passports for the first time. But you can still go to Mexico and Canada with driver's licenses, as of Summer 2008.

If you look at the US Custom's FAQ page, they're phasing in plans to require passports to cross the border to Mexico and Canada within the next two years.

Do I need a passport to go to Mexico or Canada?

No, but you will need proof of US citizenship, such as a birth certificate, and a photo ID, such as a state-issued drivers license or ID card. You are well advised to get a passport, anyway, and carry it with you to Mexico or Canada. It is the ultimate proof of US citizenship. An adult US passport is good for ten years, so if you plan a trip to Mexico or Canada, get it anyway, in case you get a chance to go to another country sometime later.

Western Hemisphere Travel Initiative
http://travel.state.gov/travel/cbpmc/cbpmc_2223.html

ALL PERSONS traveling by air outside of the United States are required to present a passport or other valid travel document to enter or re-enter the United States.

LAND AND SEA TRAVEL

The following summarizes information available on the Department of Homeland Security’s website.


CURRENTLY:
U.S. citizens need to present either (a) a passport, passport card (scheduled to be in full production beginning in July 2008), or WHTI-compliant document;
or (b) a government-issued photo ID, such as a driver’s license, along with proof of citizenship, such as a birth certificate.


LATER:
On June 1, 2009, the U.S. government will implement the full requirements of the land and sea phase of WHTI. The proposed rules require most U.S. citizens entering the United States at sea or land ports of entry to have a passport, passport card, or WHTI-compliant document.

lazlo
12-12-2008, 01:28 PM
To get one I have to go in person to the Vancouver consulate and fill out the forms and present my finger in order that they may take a print for the passport.

Evan, I just got a new passport in June -- there's no fingerprint.

You can renew your passport by mail -- you don't need to physically go to the passport office.
I had to pay a courier service to express process my passport this Summer, and they got the whole thing done in 24 hours. It wasn't cheap...

derekm
12-12-2008, 03:47 PM
I got quized everytime I flew in and out of the U.S. because I had a U.S. Visa. This was considered too unusual for a U.K. citizen and I had to explain why I ended up with one.

I had made the mistake of entering the U.S. one time by yacht and had needed a visa for doing that...

lazlo
12-12-2008, 03:55 PM
I had made the mistake of entering the U.S. one time by yacht and had needed a visa for doing that...

US Customs always marks pretentious bastards for special treatment :D

Evan
12-12-2008, 05:18 PM
You can renew your passport by mail -- you don't need to physically go to the passport office.


You are inside the country. The rules are different if you are not.



Passports
Renewing a Passport without a Personal Appearance
For many adult applicants, you can renew your passport without making a personal appearance at the Consulate. Your assistant or helper can bring everything to the Consulate for processing, saving you the trip.


You can renew your existing passport without a personal appearance if––

You were issued your most recent U.S. passport at age 16 or older and within the past fifteen years, and

You can submit your most recent passport (even if it has already expired within the past fifteen years as long as you meet the other criteria, below), and

Your most recent U.S. passport was issued for full validity and

Your name will remain the same as on your most recent passport.


If you are not eligible to apply for your passport by a third party, you must come to the Consulate yourself in person and apply. Follow this link for full details on applying in person.


http://hongkong.usconsulate.gov/acs_passports4.html


My last passport was issued in around 1968 or so.

lunkenheimer
12-12-2008, 08:15 PM
If I read that right it means that you can make an appearance at the consulate in the country you're in (Canada) to renew your US passport (I can't see all the previous posts right now, and IIRC you mentioned the drive time). So, is the issue essentially one of the travel time to the consulate not being worth the immediate gain? Since you're dual citizenship I don't know how that could complicate things (or simplify them? E.g. if you can get a Can passport in a simpler fashion than mucking around with Homeland inSecurity)

Evan
12-12-2008, 08:45 PM
If you are a US citizen it is not permitted to try and use any other passport to enter the country regardless of what other citizenship you hold. In fact it is illegal to do so and can result in a fine or even imprisonment.

The US isn't barring me from returning but they are making it difficult and expensive enough that I will not bother. Nor is it possible to do so in an expeditious manner if reason should arise. We used to vacation on the Oregon Coast and spent many fine days exploring that area in various years. Some of the people that served us even remembered my special food requirements when we would return. It's now an unattractive travel option for a number of reasons not the least of which are the changes in US border and aircraft policy. I refuse to be treated like an imbecile and a potential mass murderer with no other reason to be suspected other than that I am using public transportation or crossing a border.

I also refuse to speculate what the motives are for prohibiting such items as nail files on scheduled airline flights when it is possible and very well known by the authorities that I could easily carry on board a ceramic meat cleaver that is undetectable by currently in place technology. Whatever the motives I am not stupid but "they" seem to think I am. Further, the "hightened security" at the border is complimented by the total lack of control over private vessels sailing in and out of the San Juan Islands group in the Straight of Juan de Fuca. Anybody can cross the border undetected if they use a small boat instead of a car.

It's all smoke and mirrors and it only effective against the very, very stupid. I refuse to participate in the scam.

Incidentally, all the same applies to the Canadian authorities although, in their defense, most changes here have been pushed on Canada by the US.