Steve, nice work and thanks for the updates. I'm hoping to get back to another trial during the week.
Simon I may be interested, I do want to have another go at cutting threads however professionally made Acme should be better than what I expect to achieve. I'm also pondering building a CNC milling setup and would probably use a few worm gears in that if I go ahead. Price will of course be a consideration.
I decided to try out an approach which first occurred to me when I heard about hobbing.
Using a conventional tap held in the lathe chuck. I used a 3/4 16TPI UNF tap which I had on hand an offcut of 63mm OD alluminium round. 10 minutes or so to tidy up the round and another 10 minutes or so of hobbing and the thread is cut deeply and as a first pass looks quite passable. I'm wondering how that would work if I later bed a worm into that for the final tidy up. Possibly not up to astrophotography standards but maybe suitable for a lot of other uses.
I wanted to test how well a conventional tap would turn the gear blank and also how well it would go without having a grove already cut. Excellent on both counts. The cut as it is at the moment has a slightly raised edge on the lower side (where the cutting teeth exited the blank) but that should clean up neatly.
That looks better Steve. A good wrap around the worm to ensure good meshing at all times. Well done! Now there's just another to make.
I'm not moving on to the RA gear Dave until I'm happy with every
aspect of the DEC attempts , including how consistently I can
repeat this all.
I reckon I'm nearly there though.
The inspiration and reason for my success so far would all
be down to your work, and the work of others
Quote:
Originally Posted by hikerbob
I decided to try out an approach which first occurred to me when I heard about hobbing.
Using a conventional tap held in the lathe chuck. I used a 3/4 16TPI UNF tap which I had on hand an offcut of 63mm OD alluminium round. 10 minutes or so to tidy up the round and another 10 minutes or so of hobbing and the thread is cut deeply and as a first pass looks quite passable. I'm wondering how that would work if I later bed a worm into that for the final tidy up. Possibly not up to astrophotography standards but maybe suitable for a lot of other uses.
I wanted to test how well a conventional tap would turn the gear blank and also how well it would go without having a grove already cut. Excellent on both counts. The cut as it is at the moment has a slightly raised edge on the lower side (where the cutting teeth exited the blank) but that should clean up neatly.
Bob
Nice looking result Bob.
On a bigger diameter wheel you would have to extend the tap from
the chuck.
I've seen this done on a few webpage examples and it seems to work
well.
I also get that same exit roughness on the teeth even with the multi
scoring on the hobber.
But as you say, it does clean up after a skim on the faceplate and/or
a bit of fine wet and dry.
Oh, and the things I could make with that 63 OD alu round!!!!
Ok, enough stalling, finally I tried an ACME shaped thread.
As I thought, it was all down to how well I could shape the
tool.
An M12 x 1.75 ACME tool is a fairly tiny trapezoid to grind
and the errors were soon showing on the result thread that I
cut with it.
It was obvious the flat was too wide because I couldn't go
full depth. The flat at the bottom should match the flat at the
top. As I neared final depth I was sacrificing wall thickness, the
very thing that makes ACME a strong driving thread.
Anyway, I decided to do another hob with it and see how it
went.
Another successful self index.
Then the depth cuts, gradually adding 2 thou each time and
letting it drive around a few turns.
Polished on the clean part for a while then bored the worm and
parted it off.
The last pic shows the ACME worm that can now be swapped
with the other sleeve to try it out on the DEC axis
Steve
Last edited by kinetic; 12-05-2009 at 07:47 AM.
Reason: added text to pic 4
Well done Steve. I played with the results of my last effort again tonight, bedding the thread from a 3/4 UNF high tensile bolt into it and turning the bolt down so that I can have a play with it. So far all good.
Not a lot done this evening, I've had a few other things happening and also been fiddling with my first dew heater. No photo's tonight but thanks for yours.
....
Simon I may be interested, I do want to have another go at cutting threads however professionally made Acme should be better than what I expect to achieve. I'm also pondering building a CNC milling setup and would probably use a few worm gears in that if I go ahead. Price will of course be a consideration.
Bob
Hi Bob
So far so good, may have an Aussie supply but waiting for them to get back to me.
Found a US source. US$19.95 but minimum international order is $200... grrrrr... and freight = ?
Found a UK source. £19.95, no minimum, but freight = ?
Keep in mind the feedscrew is ~500mm long, enough for many worms and hobs. Dunno how I'll go cutting it.
Here's hoping the Aussie source comes thru.
Hi Bob
So far so good, may have an Aussie supply but waiting for them to get back to me.
Found a US source. US$19.95 but minimum international order is $200... grrrrr... and freight = ?
Found a UK source. £19.95, no minimum, but freight = ?
Keep in mind the feedscrew is ~500mm long, enough for many worms and hobs. Dunno how I'll go cutting it.
Here's hoping the Aussie source comes thru.
Just remember guys.....unless you can get the commercial ACME thread
exactly concentric on some sort of drive shaft in your 3 jaw or 4 jaw,
you will have an error transferred to your blank.
That's why I'm machining my hobs/worms. It makes them exactly concentric.
I had a few test runs with turning ACME form threads
for worms this arvo and I think this is about the best
I can get without a jewelers grinder and microscope for
getting the tool perfect.
At full depth, 10.25mm minor dia the shape looks pretty
balanced. Not perfect but close.
At least the shoulder looks a bit thicker now.
I'll try this as a hob on a blank next.
I think I'm finally there.
This one doesn't look too shabby at all.
This is a full depth M12 x 1.75mm ACME using the thread from
yesterday's post.
As in most efforts previously, self index went well.
I marked the first contact with the pre-cut groove as 0.00
on the cross-travel.
Then added cut depths of 2 thou (sorry my dials are in thou)
until I was full depth at 34 thou.
Final polishing and lapping on the section that would end up being
the worm again.
Then recovered the worm by carefully parting off the live centre end,
boring out to 8mm (so that it slips on the worm drive assembly),
and then finally parting off.
I can't wait to try this baby, it is the most snug mesh I have had
so far, and by far the cleanest teeth on the gear.
Oooooh that looks good!!
I found ACME thread a pain too. I found that the end of the tool kept rounding. Might be my technique. Getting the flat at the bottom and top is bloody hard.
Well done on your efforts.
What led you to do a 317 tooth Worm wheel?
Are you planning to run a servo unit or stepper motors?
I am watching this thread (yeah, ok "pun" intended) on the worm stuff.
I have got so many plans/designs, but the worm concept is on my brain.
I was thinking of going to a RC shop and buy some steel gears (worms etc) and giving it a go.
The idea of using a stepper motor, is sitting on my brain, just worried if it's geared high (say 100 : 1), that the stepper motor turns too slow (microstepping) creating jerkiness.
I figured a stepper motor turns smooth when running about 1/3 a turn a second.
Or are the steppers these days pretty good on microstepping?
What have you guys got planned to drive these wheels?
What led you to do a 317 tooth Worm wheel?
Are you planning to run a servo unit or stepper motors?
Brett, yes I have a homemade Bartels Stepper drive system, dual axis.
With microstepping (steps further divided into 20 or 40 microsteps
by the software) the drive is very smooth.
Mel Bartels recommends a reduction of about 4000:1 as a guide
so there is no chance of steps showing in the final drive.
My RA reduction is about 10,000:1 and very smooth but has terrible
backlash due to spur gears. Hence the need to make a good worm.
The 317 teeth is a result of purely the choice of pitch and diameter
of blank.
An earlier test on the same blank resulted in 347 teeth and a dia of 7.5".
If this all works it is simply a matter of writing in an integer value in a
script file in Mel's software to calculate arc seconds per step.
Software does the rest.....beautiful.
Quote:
Originally Posted by Spanrz
What have you guys got planned to drive these wheels?
In my case, most of the original geartrain that I currently use, minus
the last spur gears which will instead drive the worm/worm gear.
That's brilliant Steve! It's been fascinating to watch your efforts and to watch you learn-by-doing, surely the best way.
Thanks Dave ,everyone for your kind words.
It doesn't take a lot of grey matter for this dumb sparky to operate
a lathe etc. It's all down to others like yourself who paved the way
before and were decent enough to explain their journey in words and
pictures, for people like me to have a bash myself.
