Member postings for John Pace

Posted by Chris Taylor 11/10/2019 20:24:09

I am also looking at machining some bevels using Ivan Law’s
parallel depth method, but 38DP Meccano size. I’m having
difficulty following the fig.80 calculation, partly because Ivan
chose 20 tooth and 20 DP so when 20 appears in the calculation
I’m not sure which parameter is referred to. Two questions
for the experts: number of teeth on back cone PD =1/sin45 x 20,
presumably the 20 is number of teeth at the small end? And
where does this come from.
Second question: the offset for the second
cut also has a 20, which is clearly
small end N, but where does this come from.
Any help much appreciated

Hi Chris

The 20 that you refer to is the number of teeth in the gear.
and is the same pitch diameter PD as a normal spur gear.
It is unfortunate that the example shown in the book is shown as
a mitre gear as this seems to have caused much confusion over time.
The drawing shown here is of a 15 tooth parallel depth gear 30 dp ,
because the angle formed from the back cone it equals a spur gear
of 16.62 teeth 2 x .277 inch .554 inch x 30 dp ,this falls
just below the range of a No 6 cutter 17 to 20 teeth but is just
usable as a gear. The second photo shows this made gear
and you may be able to see the slight undercut at the root ,arrowed.
The second question the 20 again is the tooth number, see page
109 fig 84.

John

Hi Colin ,

The two parallel bars are piano wire and provide some spring pressure to bear against the square bar that holds the driving pins,the tension is adjusted so the boring head moves and when the head reaches its limit of travel the spring is overcome and the drive knocks off.

John

Hi
I guess this is what you have ,there is not too much needed in setting
up, the bracket holding the pins should be central around the star wheel.
Usually best to revolve the machine by hand to see the pins engage
cleanly with the wheel. I use mine on the Myford 7 only on the 2 lowest
back gear speeds ,if you try to go too fast the pins knock out of
engagement ,useful bit of tooling.

John

It is fairly obvious from the photo that a repair has already been
attempted ,the tatty chamfer around the insert no doubt done
removing the old detent ball .
These detent balls are nearly always fitted in a blind hole and the
a press tool used to peen the edge over.
It would be a mistake to find a ball that fits in the hole,if you
look at a new socket end and examine it you will find that the ball
has quite some side clearance in the hole,as these things are used in a
dirty environment debris soon finds its way into the unit and renders
it useless if you have a close fitting ball .
Using centre pops the close the hole is equally useless as it leaves an open
gap for the dirt to get in ,again examine a new one and you will see
what i mean.
The sketch here is nearly to scale with 5 mm ball made in two parts
and would require the use of a lathe to make.Doing it this way you can
assemble and test it before fitting in the existing hole with some
low strength adhesive.
John

I never pass up the opportunity to re-use scrap metal,
the main drive shaft shaft for this home built shaper
came from the broken half shaft from a 1942 AEC
Matador.

All of the sheet metal parts of this home built cylindrical grinder
were scrap material ,the main coolant tray was from the cover
between the base from my Warco lathe ,the motor mounting and
wheel guards came from the chassis of an old electrical cabinet.
The splash guards were from the drum of a tumble drier.
I suppose you will have to draw your own conclusions on
whether they are fit for purpose.

John

Hi Duncan

This gas turbine inner section NGV machined as a tryout
from prototyping wax could be used for casting purposes
if tided up a lot ,as with all castings the pattern is the part that
takes up most time,the second photo is some model engine
parts from the early 90's ,the exhaust stub the semi-circular
part with the slot through the centre required the complicated
mould seen here top left .

John

I have my Myford stand and tray set up as you have described,the
stand is packed at an angle about 1 deg and the mountings for the lathe
set so the machine is level.
I use neat cutting oil the angle is enough for the oil to drain away.
If you are using suds coolant it is still worth doing if you have a
hobby type system the container only holds about 12 to 15 litres
if the tray fills with coolant the level drops in the container and
pumped delivery slows down.

John

For a short while whilst doing a paid job i had to use some
Rocol V cut ss soluble coolant in the Myford, the photo here
shows the damage to the lathe bed that you can feel with
your finger tip not just the nail .I don't know if there was some interaction

between the cutting oil and the slideway oil that caused this .
I originally used the Rocol on the cylindrical grinder the continual
rusting problems with this have gone away with the neat grinding oil,
The rocol is now only used in the cut off bandsaw.

John

I use only pumped neat cutting oils for cutting and grinding
Exelcut 401 for turning and milling steel ,aluminium ,brass ,cast iron.
Excelcut 433 for grinding all of the same.
No rust problems ever, keeps the machines clean and oiled
I buy it from J& L the 401 is sometimes on offer in the Advantage flyer.
John

Brian good to see that the problem is solved with all parts intact.

Your post struck a chord as i had in the past experienced this similar
problem which was solved how i had described.
It was some time ago back in 2005 when i cnc'd my Myford 7,it took
me 4 years to cnc my Dore westbury mill and about 3 weeks to do the
Myford .
Seen here in the photo the stepper motor is mounted at the back of
the machine ,i made a complete new rear bracket for the lead screw with 2

preloaded ball races for the lead screw.
Rear mounting the stepper motor retains all of the functions of the manual
machine.
John

Just had a look at mine ,took off the 2 nuts and washers and the key from the lead screw and it comes away with no problems ,there is not much clearance between the slots and the studs and it may over time formed a small burr on the edge of the slots which is catching on the threads on the studs .

John

The image here is of a 12 tpi whitworth thread gauge and ground
form tool ,the USB microscope was from maplins so probably
not so great as a precision instrument,but would you really want to use
something more expensive in such a dirty enviroment.
The image shows two places where dirt or swarf is bridging between
the tool and gauge and this is after demagnitising and a good air blast
i guess this is just static attraction and would be worse in a machining
situation.
The closer in you get to the job the more distortion you see in the image
in this photo ,look at either end of the gauge .
The obvious thing to do as you already have a microscope is give it a try
and let us all know how you get on.
John

I made this unit from the drawings in Model engineer
designed by H.D. Bickley
Vol 167 no 3903 16 August-5 September 1991.
It works very well for small workshop items.

John

Posted by Vasantha Abey 01/09/2019 05:03:14

Dear,

I am from Sri Lanka and if you can let me have a copy I will appreciate that too. I tries to make a
Mitusubishi Evolution Crank shaft from a a billet of EN19 steel. I tried a 2d sketch of pin and
journal plan view on Solid works, and the curser allows the coordinates to see at the bottom.
You can divide the contour to say 60 points, note down the x,y points.

later you can write a G code program, switching y axis to z on you MS Note pad.
keep the x as 0. Of course you need a 4th axis to turn the crank shaft. This is a
very difficult process, but you can do it. The end mill on the spindle need to rise
and fall during the rotation of the dividing head. I have used a servo motor driving
a toothed belt that slips on an aluminum toothed rim tightly fitted to the pheriphery
of the divider plate. The servo motor also has a toothed wheel and with an encoder.
The cnc mill has a Centroid CNC 4 axis installed and the mill is an OKK Mill.

Remember that the pin travel like a clock hand and round the center of the journal .
On solid works 2D drawing, you have to draw at least 20 circles or more right round
the journal center and circles are in orbit. Then you can use the curser to plot suitable
cordinates on top of each circle and write a gode program. the X cordinate should be
made Z. I will soon send you the G code program I used but to day is Sunday so will
do it on Monday.

Hi Vasantha

Having done some of these type of plotting type job i know how tedious
it can become.All is not lost as you were doing it this way i will assume
that you may not know this as follows.I use an early cnc system "Compucut"
a Dos based unipolar system and an old drawing system Draft choice for
windows .The Compucut system has a file "circdata" in which
the basic units are inserted and produces a plot file ,this file is then
converted into a relative file .The file takes the form of PR nnn,nnn;
which Compucut uses " HGPL" . Using find and replace in wordpad this is
converted into the format 3R nnn,nnn,nnn; like you the the x axis is
all 000s and the y axis and z axis is using the data.
Most likely the drawing system you use will have a polygon function,drawing
this and saving the data it can be exported and the file produced is the same
as the circdata that i use ,perhaps the easy tryout is to draw an 8 sided form
and see what is produced. The compucut circdata has an odd quirk in that
the data starts at 0 deg in the 3 oclock position moving anti clockwise so to
use it for this crankpin the 1st quadrant is cut and then pasted at the
end of the file to start at TDC At 0.5 deg resolution the Compucut version
gives 720 lines for one rotation.the test piece in the photo is at 4deg and
has 180 lines only cut in wax just to tryout ,as in your post the axis of the cutter
tracks the centreline of the pin ,the pin diameter is determined by the distance
of the cutter relative to the axis of the pin.

John

Posted by ChrisB 21/08/2019 17:59:22
I doubt you'll manage to weld it with mig, you could try - nothing lost.

Back in 2010 published in MEW 166 i wrote and article on Mig welding
bandsaw blades, i have not bought a made blade for 20 + years just make
them from a reel of blading.
They last so long that i need sometimes to resharpen them.

John

Posted by Martin of Wick 19/08/2019 14:09:28

The approach I would use based on a posting above is to
lightly clamp up a washer in the gap between the rearmost two teeth. with
the chuck stationary and spindle locked, grind all the forward teeth of the jaw
to something resembling an even height and hopefully
parallel to the lathe axis, repeat for other jaws.

Martin

The jaw needs to be restrained towards the front edge so when the chuck
is tightened up the jaws will grip along the length.If you trap the jaws at the rear
there is the possibility that when the jaws grip the front edge will not be so secure
effectively slightly bellmouthed.
The photo here uses a washer and a piece of wire to apply some tension to
the front of the jaw ,this is all that is all that is needed to do this on this 80 mm
chuck .It would be fairly easy to make a more substantial clip from more
solid material if required.
The washer is cut to clear the jaw edge ,the other jaws are retracted clear
the chuck key is used to oscillate the jaw to and fro past the grinding wheel.

John

Posted by
Graham Williams 11 16/08/2019 17:19:26

Wonder what a small gear hobber will cost to make........... where is this going?

An article published in MEW 193 Sept 2012 Shows an electronic system
which is still available from Richard Bartlett ,as of last year he still had 12 of these
available in pcb form.The article show the mechanical parts that i made and will cut
spur and helical gears of any tooth number.
Obviously this requires some amount of work and expense to complete to make
this unit and also finding an 0.8 mod or 32 dp hob.
These here sell hobs i have not bought from them so have no experience
of their service.
https://www.aliexpress.com/w/wholesale-gear-hobs-for-sale.html

Without knowing the exact specification of the gear ie 0.8 mod or 32 dp if the gears
can be hobbed the 0.8 can be cut using the pcd of the 32 dp ,i doubt you would be
able to tell the difference as the error will be less than the backlash.
The photo here is a 0.8 mod 17.5 deg helical gear for an align powerdrive unit.

The gear in your photo appears to have some damage on the flanks not unlike
the descriptions shown here in the second photo taken from a gear book, the
descriptions of abrasion and scuffing would seem to apply.
For this reason it would be unwise to make and fit some fudged gear and hope that
it will run in.

John

The jaw faces are not parallel to the lathe axis use a pencil grinder held in the top slide and regrind each jaw face in turn in situ not under power, you will need to apply an inward load to the jaw to stabilize .Not much needs to be ground off mark with a felt tip pen to see the grinding along the jaw length.

John

Some useful and interesting threads in the RCME model flying forum

Engine projects
or I THINK it's all there ? By jeff2wings
and

4 stroking a Merco...
By Foxfan

If you are going to superimpose an existing valve timing
layout from another engine it is as well to remember the
Merco engines have an offset alignment from the crankshaft
to cylinder bore (Desax) so it may be wise to work this
out before cutting metal

John

Posted by Howard Lewis 04/07/2019 21:09:34

I want to cut a worm to drive a Mod 1 gear. This means that the circular pitch is pi,, unless i've miscalculated.
So effectively, I need to cut a thread with a pitch of pi mm
Have spent two days setting up, recalculating and recalculating, a spreadsheet
to cover every one of the 1278 possibles available on my lathe.
The closest that i can get is 3.165 mm. This gives an error 0.060%, which will
give a pitch error of 0.188 mm (0.0074" in old money) This seems to be a lot.
Is this likely to cause any major concerns, or is it tolerable?

Howard

Looking though Ivan Law's book gears and gear cutting on page 97 and the adjacent pages
provides some explanations on the pitch of worms.
It would not be of any use to be able to cut a worm exactly the pitch to suit the CP of the gear
(assuming that this is to mesh with a spur gear) since the worm has to be set over at an angle
in order to mesh with the gear.He does make the point that if the helix angle is low about 3 deg the
difference can be ignored.
However by adjusting the helix angle in this case to 6.9 deg the figures work out to the 3.165 mm
or .1246 inches .
As described in the book dividing the circular pitch by the cosine of the helix angle of the
worm to obtain the new pitch CP 3.14 mm or .1237 inch divided by cos 6.9 deg = .1246 in
or 3.1649 mm ,at these figures the worm would be .328 inch PCD , .407 inch OD .
It just depends if you can live with the 7 deg set over and the root diameter of about .240 inch .

I don't screw cut worms anymore , i mill them the finish is much better along with a cnc system
the pitch can be adjusted over many teeth and along with the control with rotation any size or
pitch can be achieved ,the same basic parameters need to be observed in respect of lead
helix angle and pcd.
Here is a 1 module worm and hobbed gear at 90 to 1.

John