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Posted by JG on July 24, 2008, 6:46 am
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from "David"
> Further to my last message re this problem...
> I am going to machine a component. I have done a drawing...
> http://www.revilloc.com/lens-drawing.jpg (it is 1.5MB)
> I have planned most of the machining operations, but have one problem.
> Another issue I have is that I have to have a really thin wall on part of
> the component. Slightly less than 0.4mm. This is the only clearance I
> have...
> The drawing is not quite correct, but almost all there...
> The spigot you can see in the main diameter, is about the same height
> as the
> 3mm step in the side view. The bit I am missing is that the remaining
> inside
> diameter around the spigot should be 62.2. This is my step 9, but not sure
> how to do it.
A bit late coming to this discussion and I an going to propose a radial
alturnative solution.
As you say, your drawing is incomplete and I have made some assumptions
about the missing detail but hope that I have interpreted your needs
correctly. I've done an accurate drawing and put it on my wb site as a
.PDF - see www.special-time.co.uk/drawings and select the only one
currently there.
I would not start by machining the finished size at all. I think it
would be better to prepare a billet at (say) 68mm dia. x 15mm long and
hold that in soft jaws to machine the internal dimentions.
Then I would machine a mandril at 63.85mm dia. with a suitable tapped
hole in the centre (say M6 or M8) and a clamping disc 65mm dia -
possibly with a 62.2mm reference spigot if there is enough depth to that
dia - and mount the part machined ring on that to finish the outside.
The issue of the 'tab' with the two holes could also be better served by
this method since you could mount the 68mm dia billet on you rotary
table (again with the aid of the 63.85mm mndril) and mill the 62.2mm dia
for 330° (with a 3mmŲ slot drill) finishing the precise shape needed
with needle files. You could also drill and tap the two holes whilst
still mounted on the RT.
Another radical option with regard to this 'tab' would be to fabricate
it . . . . see the section drawing at the bottom of my drawing . . . .
This would allow you to finish machine the 62.2mm dia. but would require
other work in milling the slot and finding a means to fix the 'tab' in
place - probably a cyanoacrilate adhesive but maybe a 1mm pin as well.
I hope this has given you food for thought if not a complete solution.
JG
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Posted by David on July 24, 2008, 1:49 pm
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Hi,
Thanks for this (and the drawing)...
After I posted the message initially, I had thought that I can use the
rotary table with the chuck off my lathe fastened to it somehow. Then use a
small cutter to cut the material leaving the spigot.
I would prefer to have it all as one as that will be stronger. I did try
supergluing (cyanoacrilate) the plastic one in my original photo but the
lateral force that the spigot needs to apply forced it off again. The spigot
drives the zoom on the lens so there is a reasonable force there.
The spigot itself is level with the top of the ring rather than the bottom .
My thoughts were that this obviously makes the whole thing easier to machine
as I don't need to machine on the other side to the very thin wall section.
This means that I could practically almost finish turn the whole thing in
one go, then mount on the rotary table to machine the spigot, drill and tap,
then back in the lathe to part off. All without removing from the chuck, not
that perfect concentricity is actually required.
The only thing I do need that is not on the drawing is a chamfer to the
outside top of the ring. I don't think this is critical, just a stress
relief of some sort and to not interfere with the ring that has to sit over
this.
If I get it finished (and I will) and it works, I will take a photo of the
finished article and post it. It will certainly save me £114 for a repair of
my lens or £56 if they can't repair it. I could buy another compatible lens
for £99 or an original for £150, but then they will still have this
manufacturing defect/oversight. I think making the ring from ali rather than
plastic will be much better for the lens. Aside from that, I can easily
afford a new lens, but where is the fun in that? The remaining parts of this
lens are in full functioning order and it would be criminal to throw it away
over something that can be so easily (and cheaply) repaired.
From my original photo, where you can see the original break on the tube,
that will be turned away by 3mm. The thin wall of the piece I am making will
sit inside this tube and I will superglue it. I think with the amount of
surface contact area will be enough to drive the zoom ring.
--
Best regards,
Dave Colliver.
http://www.AshfieldFOCUS.com
~~
http://www.FOCUSPortals.com - Local franchises available
>
> from "David"
>
>> Further to my last message re this problem...
>
>> I am going to machine a component. I have done a drawing...
>
>> http://www.revilloc.com/lens-drawing.jpg (it is 1.5MB)
>
>> I have planned most of the machining operations, but have one problem.
>
>> Another issue I have is that I have to have a really thin wall on part of
>> the component. Slightly less than 0.4mm. This is the only clearance I
>> have...
>
>> The drawing is not quite correct, but almost all there...
>
>> The spigot you can see in the main diameter, is about the same height
>> as the
>> 3mm step in the side view. The bit I am missing is that the remaining
>> inside
>> diameter around the spigot should be 62.2. This is my step 9, but not
>> sure
>> how to do it.
>
> A bit late coming to this discussion and I an going to propose a radial
> alturnative solution.
>
> As you say, your drawing is incomplete and I have made some assumptions
> about the missing detail but hope that I have interpreted your needs
> correctly. I've done an accurate drawing and put it on my wb site as a
> .PDF - see www.special-time.co.uk/drawings and select the only one
> currently there.
>
> I would not start by machining the finished size at all. I think it
> would be better to prepare a billet at (say) 68mm dia. x 15mm long and
> hold that in soft jaws to machine the internal dimentions.
>
> Then I would machine a mandril at 63.85mm dia. with a suitable tapped
> hole in the centre (say M6 or M8) and a clamping disc 65mm dia -
> possibly with a 62.2mm reference spigot if there is enough depth to that
> dia - and mount the part machined ring on that to finish the outside.
>
> The issue of the 'tab' with the two holes could also be better served by
> this method since you could mount the 68mm dia billet on you rotary
> table (again with the aid of the 63.85mm mndril) and mill the 62.2mm dia
> for 330° (with a 3mmŲ slot drill) finishing the precise shape needed
> with needle files. You could also drill and tap the two holes whilst
> still mounted on the RT.
>
> Another radical option with regard to this 'tab' would be to fabricate
> it . . . . see the section drawing at the bottom of my drawing . . . .
> This would allow you to finish machine the 62.2mm dia. but would require
> other work in milling the slot and finding a means to fix the 'tab' in
> place - probably a cyanoacrilate adhesive but maybe a 1mm pin as well.
>
> I hope this has given you food for thought if not a complete solution.
>
> JG
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Posted by JG on July 24, 2008, 10:53 pm
Please log in for more thread options
from "David"
> After I posted the message initially, I had thought that I can use the
> rotary table with the chuck off my lathe fastened to it somehow. Then use a
> small cutter to cut the material leaving the spigot.
That would be an ideal scenario but if you do not have a fitting you may
need to make one - even if it simply locates in the chuck recess and you
can then clamp the chuck body using standard clamps.
> I would prefer to have it all as one as that will be stronger. I did try
> supergluing (cyanoacrilate) the plastic one in my original photo but the
> lateral force that the spigot needs to apply forced it off again. The
> spigot
> drives the zoom on the lens so there is a reasonable force there.
It is certainly the best option but does pose some problems -
specifically there is no 62.2mm reference diameter
> The spigot itself is level with the top of the ring rather than the
> bottom .
> My thoughts were that this obviously makes the whole thing easier to
> machine
> as I don't need to machine on the other side to the very thin wall section.
> This means that I could practically almost finish turn the whole thing in
> one go, then mount on the rotary table to machine the spigot, drill
> and tap,
> then back in the lathe to part off. All without removing from the
> chuck, not
> that perfect concentricity is actually required.
With a wall thickness of 0.38mm you most definitely do need perfect
concentricity, and I would suggest that trying to hold it on the thin
wall section would cause you far too much grief.
> The only thing I do need that is not on the drawing is a chamfer to the
> outside top of the ring. I don't think this is critical, just a stress
> relief of some sort and to not interfere with the ring that has to sit over
> this.
The likelihood is that it is there to remove the need to undercut the
mating part so that there is no interference between them.
I've done some more drawings (still at wwwspecal-time.co.uk/drawings)
to take account of your further detail and also to show each stage of
maufacture as I would go about it. I assume that you have soft jaws for
your chuck and are familiar with the concept of a sacrificial mandril.
The very thin wall is the key problem here, that is why I propose that
you make this one of the last operations.
I recall doing something similar many years ago when I wanted to fit
very non-standard lenses (from plate cameras) to my Pentax SLR but that
also involved screwcutting thin walled items.
I'msure you have thought about it but just in case it has slipped passed
you, you _do_ intend to paint the inside of the finished item matt black
don't you?
JG
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Posted by David on July 25, 2008, 12:26 pm
Please log in for more thread options Hi,
I had a look around your site whilst I was there picking up the last PDF.
Looks like you craft some nice watch cases. I am currently working in
Matlock (Derbyshire) and just up the road from where I work, as I was
walking past, I noticed a workshop with some very nice wooden skeleton
clocks in fully working order. I have never seen anything like that before.
They were very nice and very unusual I thought.
The way I was thinking of machining it was to make the blank deep enough and
have all the machined part still sticking out from the jaws so that I don't
hold it on any of the machined surface. Hopefully, this will not present any
crushing problems.
Also, doing it this way, as I then have no need to remove it from the chuck,
I should not need a mandrel.
I don't have a fitting for my chuck on the rotary table. I was thinking of
just clamping it down then clocking the inside of the bore to get it
concentric.
The thin wall will be away from the chuck and as I don't really need to
machine the 'top' (from your drawing, the thicker wall is at the top, so the
top is the upper surface), the 62.2 can be machined all in one setting. This
means that I don't need to hold it on the thin wall at all.
To painting the item black... I can see a possibility why, but why would I
need to paint it? The location of this component will never even see light,
The outside will be surrounded by a non-rotating ring (this is part of the
rotating ring) and the inside, there is a good 3/4" before it can see any of
the actual lens tube. A problem would be is that the 0.38 wall is actually
only giving me 0.02mm clearance and painting this would be a problem. I
guess I could paint the upper thicker portion as if anything is exposed, it
will only be this part.
--
Best regards,
Dave Colliver.
http://www.AshfieldFOCUS.com
~~
http://www.FOCUSPortals.com - Local franchises available
>
> from "David"
>
>> After I posted the message initially, I had thought that I can use the
>> rotary table with the chuck off my lathe fastened to it somehow. Then use
>> a
>> small cutter to cut the material leaving the spigot.
>
> That would be an ideal scenario but if you do not have a fitting you may
> need to make one - even if it simply locates in the chuck recess and you
> can then clamp the chuck body using standard clamps.
>
>> I would prefer to have it all as one as that will be stronger. I did try
>> supergluing (cyanoacrilate) the plastic one in my original photo but the
>> lateral force that the spigot needs to apply forced it off again. The
>> spigot
>> drives the zoom on the lens so there is a reasonable force there.
>
> It is certainly the best option but does pose some problems -
> specifically there is no 62.2mm reference diameter
>
>> The spigot itself is level with the top of the ring rather than the
>> bottom .
>> My thoughts were that this obviously makes the whole thing easier to
>> machine
>> as I don't need to machine on the other side to the very thin wall
>> section.
>
>> This means that I could practically almost finish turn the whole thing in
>> one go, then mount on the rotary table to machine the spigot, drill
>> and tap,
>> then back in the lathe to part off. All without removing from the
>> chuck, not
>> that perfect concentricity is actually required.
>
> With a wall thickness of 0.38mm you most definitely do need perfect
> concentricity, and I would suggest that trying to hold it on the thin
> wall section would cause you far too much grief.
>
>> The only thing I do need that is not on the drawing is a chamfer to the
>> outside top of the ring. I don't think this is critical, just a stress
>> relief of some sort and to not interfere with the ring that has to sit
>> over
>> this.
>
> The likelihood is that it is there to remove the need to undercut the
> mating part so that there is no interference between them.
>
> I've done some more drawings (still at wwwspecal-time.co.uk/drawings)
> to take account of your further detail and also to show each stage of
> maufacture as I would go about it. I assume that you have soft jaws for
> your chuck and are familiar with the concept of a sacrificial mandril.
> The very thin wall is the key problem here, that is why I propose that
> you make this one of the last operations.
>
> I recall doing something similar many years ago when I wanted to fit
> very non-standard lenses (from plate cameras) to my Pentax SLR but that
> also involved screwcutting thin walled items.
>
> I'msure you have thought about it but just in case it has slipped passed
> you, you _do_ intend to paint the inside of the finished item matt black
> don't you?
>
> JG
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Posted by JG on July 25, 2008, 2:19 pm
Please log in for more thread options
from "David"
> I had a look around your site whilst I was there picking up the last PDF.
> Looks like you craft some nice watch cases. I am currently working in
> Matlock (Derbyshire) and just up the road from where I work, as I was
> walking past, I noticed a workshop with some very nice wooden skeleton
> clocks in fully working order. I have never seen anything like that before.
> They were very nice and very unusual I thought.
Seeing a wooden skeleton clock was the initial inspiration for me
getting into watch/clock-making and discussion on the alt.horology
newsgroup made the whole thing take on a life of its own!
If you looked at the detailed drawings you can see that I am familiar
with machining thin sections even in wood! The bezel ring recess leaves
a 'wall' at 0.25mm thick and the ring itself is 0.3mm thick. Stainless
Steel stem tubes are often 1.6mm dia with a 1.5mm bore. Dials are 0.3mm
thick in the centre and between 0.5 and 0.7 on the outside.
> The way I was thinking of machining it was to make the blank deep
> enough and
> have all the machined part still sticking out from the jaws so that I don't
> hold it on any of the machined surface. Hopefully, this will not
> present any
> crushing problems.
> Also, doing it this way, as I then have no need to remove it from the
> chuck,
> I should not need a mandrel.
I only hope that my suggestins have given you 'food for thought'.
Cutting the chamfer won't cause you any problem with the way you propose
to do the job and my only concern is that you won't get a fair-face to
the 'top' if it is simply parted off.
> I don't have a fitting for my chuck on the rotary table. I was thinking of
> just clamping it down then clocking the inside of the bore to get it
> concentric.
That could be your next 'Project' :)
> The thin wall will be away from the chuck and as I don't really need to
> machine the 'top' (from your drawing, the thicker wall is at the top,
> so the
> top is the upper surface), the 62.2 can be machined all in one
> setting. This
> means that I don't need to hold it on the thin wall at all.
> To painting the item black... I can see a possibility why, but why would I
> need to paint it? The location of this component will never even see light,
> The outside will be surrounded by a non-rotating ring (this is part of the
> rotating ring) and the inside, there is a good 3/4" before it can see
> any of
> the actual lens tube. A problem would be is that the 0.38 wall is actually
> only giving me 0.02mm clearance and painting this would be a problem. I
> guess I could paint the upper thicker portion as if anything is exposed, it
> will only be this part.
Just my cautious approach to anything 'photographic' but I would also be
concerned about oxydation which would be minimised by the application of
paint - I doubt that acrylic paint would be as thick as 20 microns but
you could try candle smoke to take away the 'bright' alum finish.
I look forward to your photo's of both production and finished article :)
JG
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