Member postings for John P

Hi
Seeing Howard's post about the flaming rag ,at Worthing
depot it was common thing during the cold weather to
use a paraffin rag on a bent piece of welding wire
on Mk1 Leyland National buses ,the manifold heaters
were a heater coil that had a fuel supply that were a
common problem with fires and were mostly disconnected
hence the burning rag ,with the layout of these vehicles
the usual procedure was to drop out the air filter stuff up
the rag crank over and off you go ,one day i was on a late turn
and the lad who was on the morning shift tried it and left the
air filter element in place ,set fire to the air filter which spread
to the rest of the bus ,when i came in later in the day all that
was left was the burnt out carcass , happy day's.

John

Hi Dave
What you have described is very similar to this cnc cutter grinder
that i made some long time ago .the basic framework would
function just as well for a manual type machine and is made from
2 pieces of 6 inch channel welded together in an "L" type shape.
I see that you have not got a dovetail cutter ,Aliexpress sell these
quite cheap and would be needed for this type of construction.
One of the big problems with these machines is the grinding dust
on the slides ,this machine that i have has oiled slides and has been
running 14 years with no problems.It was serialised in MEW in
around 2008 i have all of the drawings in jpeg form if you
are interested.

John

This might be of interest to some on here who have multiple
thousands of photo's in albums .

This is what has happened to to the members photo's
on the Model flying forum.

"David Ashby - Moderator
Posted February 3

We've learned that although all photos will come across to the
new forum, albums won't. In other words you won't find your
photos neatly segregated in the gallery area on the new platform.

I don't know how important this will be to forum users, and
assume the majority just use the albums for posting, but
thought I should mention it now I'm aware."

Seems as if the photo's are all on this site in a community
jumble .
Brave new world

John

Posted by
Howi 12/02/2021 10:02:38
to put an end to this nonsense lets have a poll, change the forum or
leave as is, I would suspect the latter.

Do you think that they would really be interested in your opinion
or mine.

From Jason's later post

At 12/02/2021 10:16:26

Maybe, maybe not Michael as it all depends on (how MTM decide to
customise the forum for our use), take a look at the RCM&E one that
Ketan linked to as that is in the early stages of what we may end up with here.

From the part in brackets it would seem the decision has already been made ,
they just have not announced it yet.

John

The last part of this post by

Neil Wyatt 11/02/2021 13:25:38

If that isn't 'broken' what is?

There will be complaints and a period of adjustment, but I very
much doubt that after a month the complaints will be anything
like those that we have had.

Neil

Reading between the lines of his post and seeing that RCME
are in the same publishing group, it looks as if a decision
has already been made.

What next , no paper magazine on line publishing only ,
stick on a pair of goggles and go for a tour around the virtual
Model Engineer exhibition.

John

Hi

Anyone on here also uses the RCME model flying forum ,used to have a similar layout to this one ,has been changed over this last few days , go and have a look at it , be grateful for this one and hope there are no plans to change to a similar layout ,it looks bl**dy awful.

John

A little off topic from to OP's original question, however here are
a couple of interesting videos for end mill
grinding ,the first one a cnc machine.

www.youtube.com/watch?v=qxU0K-TmEvI

The second one here is a mechanical unit and
below is the patent explaining how the mechanism
works

www.youtube.com/watch?v=Pb14T-bDB1g

US2503926A - Spiral grinding machine - Google Patents

John

I just wonder if this style of gear seen here would be more
suitable for Joe's application

This video shows these spiroid and helicron gears which can be made
with zero backlash.
https://www.youtube.com/watch?v=gRriAf5snqs

A standard hob is not quite the correct profile as these spiroid and helicron
gears have an asymmetric thread form,however as can be seen
here a test gear hobbed using a 1 module cutter ,the worm would
fit in about the 11 o'clock position and have about 5 teeth in mesh at the same
time and are much stronger than a conventional worm wheel at the same size.
This gear was cut as a trial only in prototyping wax.

John

Posted by John Haine 01/02/2021 21:18:18

I'm just going to dive in here and probably hit my head on the bottom but...

If you were hobbing a gear you would set up the hob so its axis was parallel to the gear blank but not in the same plane, with the spacing between the hob axis and the blank axis such that when you feed the hob sideways, with both the hob and the blank rotating, the hob teeth will but to the full depth when the the hob has traversed right past the blank.

You can't do that with a worm wheel, but maybe you should be setting the hob axis co-planar with the blank and the axis spacing to get the required depth of cut, and feed the hob along its axis to engage with the blank? That way the hob should be cutting to the full depth in one pass and you should be able to avoid cutting away the teeth you just formed.
John

Hi John

I think i can see what you are thinking about here .This
illustration here fig 38 i think shows this method that you
described ,i think this is done in this way more for
speeding up production than anything else and for
gears of large pitch.
There should be no reason for any of the teeth to be
cut away providing the calculated sizes are adhered to.

You would need a specialized machine to be able to cut
a wheel in this way ,a bit beyond the average shed men.

John

Hi Joe

Referring back to this here;
-----------------------------------
John, then what gets me is - refer your comment:

Getting back to your gear for 158 tooth on a pcd of 116.13 mm
the normal od 117.60 mm the blank od should be 118.87 and
the tap/hob should in feed from this diameter by 2.159 mm.
The cut width across the face of the gear at this should be
as measured 10.80 mm .
-----------------------------------------------------

I had made a small drawing of this gear the only important
features are the pcd which as calculated is 116.13 mm
which will have a normal od of 117.60mm

You can check this by the normal method for gears
by adding 2 teeth to the calculation.

For PCD

To recap 1 /11 = .0909090901 inch from my
calculator x 158 (tooth) = 14.36363636 inch
divide by Pi = 4.572087456 inches or 116.131 mm

For OD

Adding 2 teeth 1 /11 = .0909090901 inch from my
calculator x 160 (tooth) = 14.54545454 inches
divide by Pi = 4.62996198 inches or 117.60 mm

I have just left the numbers as the came off the calculator and
not rounded them off.

I think there is little doubt that this should be the size the
blank should be with no additions to increase the tooth depth.
The amount that i added ie (the blank od should be 118.87)
can really be any size within reason provided that you
ensure the cut depth is correct relative to the PCD and the
Normal OD.

Adding some extra material to the normal OD allows the
root of the tap to scallop out the extra diameter of the gear and
provides some extra material for the worm to work on.

You will continue to be able to cut the 158 tooth until that
you get to a point where the the tooth will eventually thin
out and completely vanish .I know i have done this
myself , i tried to cut just a few day's ago a 7 tooth
pinion but had not noticed that i had set 70 tooth,
i thought it was odd that i seemed to be cutting
a nice smooth groove where there should have
been teeth.

It has to be remembered that using a tap as a gear hob
will not produce a gear that will resemble a gear cut with
a proper gear cutting hob .

The 1 st photo here is a 90 tooth wheel cut with a 5/16 BSW
tap using the same calculation method it looks very similar
to your cut wheel.
These type of wheels are not well suited for power
transmission and may not be suitable for the application
you have in mind.

The 2nd photo here is a worm wheel that would be suitable to
transmit power cut with a 0.9 module hob and is overcut
the calculation for the size was about 53 1/2
tooth but was cut at 56 tooth ,the target tooth count was 60
but the tooth shape was becoming too degraded on a test piece
and 56 was about as far as i was prepared to go to be safe.
The difference in the shape of the teeth can clearly be seen
in comparison with a tap cut wheel.

John

Posted by Joseph Noci 1 01/02/2021 05:51:47

Pete, if I extrapolate your 1 thou error, for a 158 tooth gear, it give a 4 mm 'error; after once around the
blank, so I would need to increase the blank diameter or reduce the number of teeth - the latter being no
problem.

Hi Joe

You do not need to adjust the size of the blank to allow for the 1 thou error,
as your hobbing unit cuts the number of teeth that it is set at , the 1 thou is
removed as part of the cutting action but is not accumulative ,it would
be a different matter if you were "free hobbing" as the tap would be driving
the work and would then end up with more teeth than required.
It is for this reason that most attempts at free hobbing unless they are pre-gashed
end up failing.

I should have pointed this out in an earlier post ,the sketch here shows
the PCD of the gear blank , the distance between the top of the
tooth of the tap and the root is divided and used as the reference for the pitch
line for the tap and the calculation for the in feed made from this.

Aliexpress have a fairly large range of gear cutting hobs and free shipping to
Namibia .

From your later post at 10:22:41

Afraid I did not understand that...I realise that with the driven HOB process, you will get the number of
teeth, but that number of teeth will only fit properly on a circumference if that circumference is correct...And
that is the issue here - I am trying to calculate what my gear blank diameter should be. If the diameter is
not correct you simple erode all the teeth down to naught eventually while hobbing..
-------------
No that is not true ,within certain limitations the pitch circle diameter can be altered for instance
herein this photo ,the outer ring has 36 tooth in order to fit 3 equally spaced gears the sun
gear has to divide into the 36 by 3 in order to do this.This could be 6,9 or 12. As 9 was chosen the planet gears need to be 13 tooth .
Fitting these in diametrically opposite leaves a space for a 10 tooth gear,in order to fit in this
space the sun gear has 9 teeth cut on a 10 tooth blank ,the effective pcd has changed
along with the profile shape of the tooth which just uses a different part of the the same involute
curve.

Getting back to your gear for 158 tooth on a pcd of 116.13 mm the normal od 117.60 mm
the blank od should be 118.87 and the tap/hob should in feed from this diameter by 2.159 mm.
The cut width across the face of the gear at this should be as measured 10.80 mm .

I think that these measurements agree with what you have ,the sides of the teeth will always
be degraded to some extent but should be clean within the working zone

John

Hi Joe

I just picked out the 168 tooth as an example , i think that when you
try to hob down to a size and get a tooth count in the way that
you tried it is easy to run through and past the diameter you need.
The situation when hobbing with a tap is more critical than
when using a gear cutting hob because of the shape
of the thread profile .
I had cut a similar type of wormwheel only a few day's ago with a
5/16 unc tap using the same calculation method and it worked out ok.
You just need to know how far to feed in from your 120 mm diameter
to get the tap in the correct place for 117.6 Pcd.

John

Hi Joe

Try 123.48 mm as the Pcd for 11 tpi tap and 168 tooth.

1.000 inch / 11 = 0.09090 inch x 168 = 15.272 inch
divided by Pi = 4.8614 inch = 123.468 mm
As this is is the pcd you would need to add
some extra about .059 inch or 1.5 mm for the OD size and
some additional material if you want the wheel to wrap
around the worm.

It is fairly close to your 118 mm size.

John

Going back to the OP original question .

"I'd now like to move the table through minutes and seconds
( to be precise 19° 3' and 12". I can't work out how to do this.
Could someone please talk me
through it in a Pooh-Bear-of-Little-Brain-speak?"

I think there is little doubt from the many replies that there
would be a slim chance of obtaining an accurate position
of 19° 3' and 12" simply because of the mechanical errors
within the rotary table and also being able to count using
the existing hand wheel set up would be difficult to keep track of .
As has been mentioned before the stepper motor route would
be most likely to be able to count with some accuracy.

My own cnc rotary table has a worm and wheel ratio of 75 to 1
and connects to the stepper motor with a toothed belt ,as part
of some alterations which included regrinding the morse taper
some additional drive pulleys have been made, these also
have some secondary functions on some other machines.
In doing this the rotary table can be between 75 to 1 ratio
and 142.5 to 1 with the pulleys that i have at this time.

Just playing around with numbers on this table using a 10 tooth
pulley on the stepper motor and a 72 tooth driving the worm
would make the table 540 to 1 ratio in whole step (200)would equal
108000 steps per rev .Since there are 1296000 seconds
in 360° divide by 12 to equal 108000,so a single step now
equals 12 seconds . 19° 3' 12" = 68592 seconds divide
by 12 for 5716 motor steps .

It is unlikely the rotary table will be accurate but at least
the count will be correct.

For a 90 to 1 table the 72 tooth pulley is changed to
60 tooth for the same count.

Probably too much work to set up if you don't already have
something like this already.

John

Posted by SillyOldDuffer 17/01/2021 10:41:32

Be careful repurposing second-hand pressure vessels because their pressure ratings aren't guaranteed. In particular disposable bottles are lightly
made because they don't have to withstand the repeated inflations and deflations that cause metal fatigue.

Rechargeable pressure vessels are stronger and have a limited life after which they are withdrawn before they become dangerous.

As always level of risk depends on the circumstances. Occasional recharging of a small second-hand bottle at reduced pressure in a home workshop
is much safer than repeated recharging to full pressure of a large time-expired bottle in a busy factory.

As a matter of interest, does anyone know what happens when an old bottle fails? Copper boilers as used on 'our' steam locomotives leak and split
rather than explode because the copper and joints both give way gradually. Steel is much stronger than Copper but likely to shatter. So although steel
vessels hold a lot more pressure they fail in a blink and the pent up energy is released all at once in an actual explosion. I vaguely remember reading
gas cylinders are weakened at the neck so the top blows off and they vent upwards. This in expectation they are stored vertically bottom down and
can't take off like a rocket.

Anyone tried doing a hydraulic test on an old disposable gas bottle to see how safe they actually are? Harder to test than a locomotive because gas
pressures are higher, for example Propane about 200psi and Carbon Dioxide 900psi. Argon could be at 3500 psi.#

Dave

# This implies it's safer to repurpose an Argon cylinder for reduced pressure work than one that contained propane!

-------------
The Bottles mentioned in my last post have a maximum rated pressure of 165 bar
2,400 psi ,i would not consider these to be lightly made ,if you cut one
open the wall thickness is at least 3/32 inch or greater.

Pressure of propane gas at 20 deg C is 7 to 9 bar.
Of course if you happen to live in Death Valley you would need to observe that the gas
pressure would increase ie at 50 deg C is 15 to 19 bar.
Less for butane however at 50 deg C butane pressure rises to 3 to 7 bar, 103 psi,
the throw away camping gas containers that butane is supplied in is 0.017 inch
wall thickness.

Air line pressure used in these mig containers is about 115 psi .
Unless you make a pig's ear of soldering on the fittings these things are no less
safe than using copper for the pipework or even plastic and it is as well
to point out the the the supplied air tank with the compressor is a great deal
thinner than these mig bottles.

When the first model gas turbines were sold by JPX in France
these run on propane and used an aluminium container as a fuel tank a
similar size to the mig gas type bottles but very much thinner ,having had
the opportunity to repair one of these engines and examine these parts
the container for the gas was so thin you could easily press in the
sides when empty.

John

I reuse my old mig and other pressure bottles,when they are empty
i drill out each end, the paint seems a bit tough so i chuck them into the
wood burning stove and burn off the paint .
Seen here used as a water trap on the airline system and in the
next photo the adapter fitting is silver soldered in the top,
the supply comes in through the middle and exits about 2/3rd's
down via an elbow which spins the air inside the bottle.the air exits
though the top .a short piece of pipe at the bottom collects the
water to drain off.
Also used here in the photo as a refillable propane bottle for
model gas turbine starting about 75 % liquid gas filled.

Apart from that they are useful pieces of steel tubing ,why chuck them away.

John

Posted by DC31k 31/12/2020 10:49:04

That is very good. Is the connector providing the drive in lieu of a dog?

I have seen boring heads used horizontally and stationary in the tailstock for taper turning (saves offsetting
and resetting the tailstock).

I think the same arrangement would work for between centres boring (i.e. it does not matter which end of
the bar the boring head is). Is that correct?

Hi DC31k

The Dore boring head is made to fit on a Myford nose in the previous photo
this is mounted on an arbor held in the Warco chuck ,the boring head
provides the drive for the boring bar via the articulated joint is seen in this photo.
It is important that the joint in in line with the slides of the boring head,as the
boring head is adjusted the boring bar runs eccentrically to increase the cut depth.
The boring head can only be used at the headstock end and the tailstock
providing the support for the other end of the boring bar.
This was not my own idea but was seen in MEW issue 168
page 56 by Ted Barclay in which showed an amalgamation of a between
centres boring bar and boring head .

John

This combination of a boring bar and boring head works well ,with the cutter at half way along the bar .001 adjustment on the boring head = .0005 at the toolbit.. The normal boring tool fitted in the boring head is replaced with an articulated joint to connect to the boring bar ,you can just about see the Dore boring head and connector in this photo.

John

Hi

My Myford chuck is mounted in a similar way on a screwed
fitting on the rotary table ,to prevent it unscrewing during milling
operations you only need a long enough tee nut a piece of
studding and a hose clip or three fixed together as in the photo.
The tee nut will slide in and out to suit the diameter of the chuck,
the assembly is biased towards the undo direction as the
hose clip is tightened.You can mill in any direction you wish to.

John

Hi

Is it one of these lathes in this photo here ,have the user manual usual far east type of thing but has all of the information needed ,send pm with e mail and i can copy it if you need it.

John