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  #21  
Old 09-04-2009, 05:51 AM
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theodog (Jeff)
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Good onya Steve.
Sorry I've just caught up with this thread.
You've moved ahead and had much success. Unfortunately work committments have slowed my progress to a stop, but with my hol's here I will start on my spidle and now have a high standard to aim for.
Well done.
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  #22  
Old 12-04-2009, 02:58 AM
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MrB (Simon)
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Quote:
Originally Posted by Karls48 View Post
So how do you calculate diameter? I’m casting my blanks from scrap aluminium.
Not scared of a little math?

I've scanned a few things you might find useful, also found a few PDF files I'd saved from the net over the years... put them all together in a zip file that you can download here: worms.zip*
Caution: 10MB!

Note that the most useful of the files in the zip are in XPS format.
XP with IE7 can open this format, as can Vista.
Otherwise download XPS Viewer from Microsoft HERE (~2 MB)

* File will be removed in a week or two.
If someone else would like to host it more permenantly, please feel free.
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  #23  
Old 12-04-2009, 10:04 AM
snowyskiesau
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Quote:
Originally Posted by MrB View Post
Dave, that mount is inspiring!!
I have to get back out into the workshop one of these days.
I found Dave's great site a couple of years ago while browsing for astronomy stuff.
I partially blame him for me now having a lathe and a mill in the spare room
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  #24  
Old 19-04-2009, 08:14 AM
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kinetic (Steve)
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Quote:
Originally Posted by MrB View Post
Not scared of a little math?

I've scanned a few things you might find useful, also found a few PDF files I'd saved from the net over the years... put them all together in a zip file that you can download here: worms.zip*
Thanks Simon, very helpful link.
Most of my previous reference URLs condensed into a single zip.
Very handy! I'll try and upload it to my site and see if it can handle 9mB!


Dad showed me a few Engineer's Notebook pages similar to some
of those.
I'm currently digesting a lot of that theory before I dive into
making the serious blanks.
Interesting where they say even 1 thou error on any worm face
can cause as much as 45 arc sec error. After polishing/ lapping it can be
minimised but it pretty much says your wasting your time if the
disk is less that 6 inch diameter and the hobbing method so-so.

Steve

Last edited by kinetic; 19-04-2009 at 08:28 AM.
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  #25  
Old 24-04-2009, 01:51 PM
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kinetic (Steve)
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1st go at a proper blank

Hi,

today I started to get serious and try my first blank.
I started by turning an M12x 1.75 pitch metric thread
with a 60° tool.
My only variation was to only cut it about 3/4 of full depth
so that there were still flats at the top.

I also spun the cross travel to 29° so that the thread cutting
was only being done on one side of the tool to stop chatter.
This worked really well and cut a very clean thread.
After several dozen passes at the same final depth, it was
very smooth to the eye and dead on concentric.

(Depth of cut was only added with the top slide not the cross
travel).

I cut a long thread so that part could be the final worm and
part could be the 'hob'.
I scored the hob section again with my dremel to make it
have cutter flutes as previous.

The blank was machined concentric previously and the spindle
fitted to the toolpost.

After hobbing I drove the worm wheel blank to the 'worm' section
of the M12 and bedded it in with cutting compound for an hour.
It ended up quite a smooth job but slightly off centre as you
can see by the pics.

The beauty of this is that I can turn it down and have another go
This diameter, again, self indexed by pure luck, no maths was
involved.
It ended up having about 275teeth and a diameter of 148mm.

Steve
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  #26  
Old 25-04-2009, 06:46 PM
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kinetic (Steve)
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And now a go at a proper worm

Next I had a go at making a worm and housing block.

To start I turned the M12 hob/worm section down to have two
straight end shanks.
To keep everything concentric all of the next few steps had to
be done without removing it from the chuck to keep the worm
dead true. Even self centering chucks fall down at this.

I bored the final worm out to just a smidge over 8mm diameter.

This was then a snug fit over an 8mm piece of steel from an industrial
photocopier.

This 8mm would be the internal shaft the worm slides on to and
gets locked to it with a cotter pin.

I turned a shoulder to fit a ball bearing race and also an M6x1.0
thread for a nylock nut. The thrust race also is clearance on
this shaft.

Next came the housing blocks that the worm assembly would
rotate in.
I machine faced this block in the four jaw and then bored it
to suit the bearing one end and a brass bush the other.
After cutting them down to final size I then milled the rough
face where the hacksaw cut was.

Finally, all assembled except for the worm left off the sleeve
and the blocks not bolted down to a solid plate.
That's the next job.....

Steve
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  #27  
Old 02-05-2009, 12:04 PM
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kinetic (Steve)
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Testing on the DEC axis of the homemade GEM

Finally I got to test one of these serious blanks in a
real situation.

Just to finish off the worm housing it was fitted to alum
plate and a bracket made to adapt it to my DEC axis.

I also re-arranged the thrust bearing/end bearing so
tightening worked better. Had to re-turn another M6 for the
end nut. PIC 1

The finished bracket with slotted holes and set screws for
mesh adjustment shown here : PIC 2

Pics 3 and 4:
Installed on the DEC axis and in mesh.
A thrust plate locked to the DEC shaft is immediately beneath
the worm gear, which without any clutch pressure, the worm gear
freely rotates.

I drove this arrangement using a battery drill stuck on the end
straight shank of the worm.
Drove nice!!!!!!!!!!!!!!!!!!!!!!! :

Steve
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  #28  
Old 02-05-2009, 09:14 PM
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MrB (Simon)
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Good stuff Steve.
Keep posting, love reading about all stuff DIY
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  #29  
Old 03-05-2009, 08:47 AM
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kinetic (Steve)
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Quote:
Originally Posted by DaveGee View Post
I turn a groove around the circumference of the wheel with a tool radiused to the root diameter of the screw. Here is a link to some photos...

This allows for deeper meshing of the worm/wormwheel. it also allows a straight cut cutter to keep meshed during the cutting.
Dave, I think this is the biggest stumbling block for me.
The worm/wheel never looks completely meshed.
I have never done this pre-hobbing groove yet.
Next one I try I will give this method a go.
Cheers.

Steve
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  #30  
Old 08-05-2009, 07:12 PM
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kinetic (Steve)
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Radius cut on a blank

I tried another blank with a radius cut in the circumference
as per Dave G's suggestion.
I attempted to make this radius the thread root depth,
again as Dave suggested.

A few pics of this week's progess.....

Pic 1 shows the index/faceplate I use to bolt blanks to
so that machining an outer diameter and inner bore are
perfectly concentric.

Pic 2 is the blank ready to start, along with radius cut.

Pic 3 is the first teeth beginning to cut and 'self index'
Note the first points of contact are both outer shoulders
of the radius.....this shows that my radius cut was too small.
There is no sign of any point contact on the centreline yet.
(this pic was dark because the flash didnt go off...so I histo
stretched it ...hence the grainy b/w

Pic 4. close up of the self index error.....obviously the diameter
was wrong...note the 2nd smaller set of cuts.

Pic 5. It was obvious that the self index hadn't worked out.
You can see the radius has now got teeth cut almost through
all the way so that the first points of contact on the shoulders
almost meet up.
I decided to stop here and not go any deeper.

One thing learned from this try was that the hobbing was smoother
because it was trapped between the shoulders.
I will now skim this all off and have another try to get the root thread
radius more accurate.

Steve
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  #31  
Old 08-05-2009, 10:14 PM
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hikerbob (Bob)
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Thanks for the inspiration

I've had my first go at cutting a worm based largely on idea's gather on this thread (and some previous research).

I used slice of 160mm round for the blank and the thread out of a car jack for the hob/worm.

I roughly machined a grove in the rim of the blank to try and increase the contact area. I ended up with 165 teeth (if my count was correct) and the mesh up seemed to go well. The cut's in the hob were done with a thin cutoff wheel in the angle grinder. I did not do any pre-indexing on the blank.

The support for the blank is part of an old Subaru gear box cut off and welded to another slice of the 160mm round. I've used holden trailer bearings because I had some and I figured that they are designed to cope well with a mix of thrust and side load. I machined the shaft for the support post out of an old trailer axle. I still need to set up a means to lock the shaft when I'm fitting a blank (and removing a worm gear).

I had not prepared the jack screw well enough. I should have machined a shoulder into it at the end held in the lathe chuck to stop it working it's way back into the chuck. I also should have used less side force, I broke the jack screw (thankfully at about the time I was getting ready to stop cutting). I was fortunate that the pieces included the section to be used as the worm. I'm not sure if this worm will go onto a mount but I'm planning to finish it for the learning exercise and if it works well enough I might use it.

I may have a go at cutting my own worm for a future worm gear but my screw cutting skills are not well developed yet.
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  #32  
Old 09-05-2009, 06:18 AM
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kinetic (Steve)
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Bob,

thanks for sharing your results.
The Acme thread certainly looks far more suitable in shape to my
results with plain metric.

One thing though, looks like you have a big distance out from the chuck
and live centre.

You only really want to have just enough or the hobber will flex away
from cutting as you apply cross travel. I noticed this happens on mine
and it will take ages for the new cut to actually develop a deeper
thread. I use 2 thou cuts and after about 10 revolutions and cutting
compound it seems to be ready to add another 2 thou etc etc.

Was the jack thread hardened? I'm going to try turning up my first
M12 x 1.75 or M16 x 2 ACME thread soon.

Steve
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  #33  
Old 09-05-2009, 07:57 AM
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hikerbob (Bob)
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Steve definately to far out from the chuck. I do need to do the hob set up differently.

Judging by the way the screw thread cut it was hardened somewhat.

I tried to buy Acme thread a while ago but the minimum length I found at the time was far to long for what I wanted to pay. I think I noticed some on the Minature Bearings site yesterday so I'll have to go back and check that later.

I do need to learn some more about thread cutting but to date I've only tried cutting one thread which worked but with a very rough finish. I've also misplaced one of my gears for the lathe and it's not readily available as a spare (but can be ordered if I ring sydney and get them to get it from the manufacturer.

It was a very satisfying experience to turn up a worm gear, I'm enjoying the learning.

Bob
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  #34  
Old 09-05-2009, 10:43 AM
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kinetic (Steve)
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Quote:
Originally Posted by hikerbob View Post

I do need to learn some more about thread cutting but to date I've only tried cutting one thread which worked but with a very rough finish. I've also misplaced one of my gears for the lathe and it's not readily available as a spare (but can be ordered if I ring sydney and get them to get it from the manufacturer.

It was a very satisfying experience to turn up a worm gear, I'm enjoying the learning.

Bob
Thread cutting is well worth the effort Bob if your lathe is capable
of it. Mainly because, compared to a bolt or manufactured all-thread
stud, cutting your own will ensure it's concentric.
I have noticed all thread stud can be terrible quality as far as
concentricity goes.

Satisfying?.....you betcha...especially when you see it working

Steve
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  #35  
Old 09-05-2009, 10:53 AM
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Steve my lathe is capable of the work although it's got more flex than I'd like. I've got this machine (but branded differently) https://www.machineryhouse.com.au/Pr...stockCode=L159

I'm working my way through improving my skills. I recently added a coolant pump which had made a real difference. I discovered Trade Tools had them at a reasonable price. The drip tray is not a great shape for return the coolant but it's working well enough.

Bob
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  #36  
Old 09-05-2009, 11:03 AM
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Quote:
Originally Posted by hikerbob View Post
Steve my lathe is capable of the work although it's got more flex than I'd like. I've got this machine (but branded differently) https://www.machineryhouse.com.au/Pr...stockCode=L159

I'm working my way through improving my skills. I recently added a coolant pump which had made a real difference. I discovered Trade Tools had them at a reasonable price. The drip tray is not a great shape for return the coolant but it's working well enough.

Bob
Bob, flex in the main travels?....because you can adjust that to a minimum?
Looks nice...I wish I had the mill head!
With thread turning I highly recommend the 29° method (look back
earlier in this thread or just google it). Makes a FAR cleaner thread.

Hardest part of making a good thread I reckon is grinding a good tool
for it...why do ya reckon I'm scared away from ACME

Steve
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  #37  
Old 09-05-2009, 08:01 PM
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kinetic (Steve)
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a better radius cut

Today a better radius groove on the blank.
This self indexed better.
A nice shaped thread and depth too.

This blank ended up being a 7.5" dia with 348 teeth
at M12x 1.75 (STD Metric profile)

Steve
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  #38  
Old 10-05-2009, 12:01 PM
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I'm going to be trying this sometime in the future.
My lathe has a precision ground 16 x 1.5mm Acme feedscrew, trying to locate a replacement to use as a worm and hob... it's about 500mm long.
With the largest blank I'll be able to turn in my lathe(180mm), I should be able to get 360 teeth at 1.5mm pitch.
If I do manage to find a replacement feedscrew, would anyone be interested in a cut length?
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  #39  
Old 10-05-2009, 06:07 PM
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a better radius cut Part II

Another attempt here.
Metric Std profile again, M12x 1.75

As close to a full depth cut from what I can judge.
Worm was lapped with polishing compound here for
about an hour.
Certainly looked and felt snug on the worm section
of the hobber.

Steve
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  #40  
Old 10-05-2009, 06:23 PM
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DaveGee (Dave Gault)
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Quote:
Originally Posted by kinetic View Post
Certainly looked and felt snug on the worm section of the hobber.
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.
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