Member postings for John Pace

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

Posted by Mike Waldron 03/07/2019 11:25:25
Using a slitting saw to cut four slots in one end is fine, with indexing gear, but how easy would
it be to securely, and sufficiently accurately, hold the now split end to slit the other?
Has anyone ever tried this? If so could you share your experiences please?

Hi Mike,

The collets seen here in the photo are for grinding 4 facet drills
on a Quorn grinder,they are an adaption of Derek Brown's four
facet system that was in the model engineer many years ago.

They are similar to what you have in mind for these internal collets.

As you can see these have 8 saw cuts ,after all of the turning
was completed a short piece of round material is placed
in the bore and the job held in a 4 jaw chuck on the dividing head.
The jaws of the chuck are at about 45 deg to the horizontal to miss
the slitting saw ,the saw is fed in close to the chuck and the cutting
is done away from the chuck ,this is particularly important when the
job is turned around and reset to do the second set of
four saw cuts.
The short piece of round material provides enough stability and
clamping force for the chuck to hold the work securely.

The material is silver steel unhardened,the largest is about 3 1/4
inches long and will hold up to 1/2 inch drills ,the smallest about
1 1/2 inches long and will hold a .5 mm drill.

John

Posted by Paul White 3 30/06/2019 13:22:09

I would like to ask how you measure the helix of the cutters for sharpening.
I have tried all manner of devices (mechanical ) but have failed miserably .
The area I am trying to address is that of sharpening the sides of small end
mills when the usual mechanical guide does not work.
your use of an electronic solution looks to the answer but the helix variation
has me stumped.

An article that was in MEW 143 through to 147 "A cnc cutter grinder "
may be worth a look,it describes the construction of a machine and its use.
The photo here shows a 3/4 inch long endmill and a 3 mm 3 flute carbide
endmill alongside ,both have been sharpened on this machine.

It is important that the cutter should follow the original lead of the cutter, as
can be seen the lands on the large cutter form a parallel edge along the length
of the cutter,any deviation from this would mean the clearance angle would
change or the cutter would become tapered.
Some cutters have the lead engraved on the shank ,as can just be seen
the imperial cutter is marked 5.440 inch and the metric has 56 next to the
small triangle indicating the lead is 56 mm.

Much more sophisticated machine seen here...

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

They use the same method as i do to measure the cutter but their
system is much easier to use.

John

This is the method i use when holding thin and awkward
and irregular shaped pieces for machining.
This part of a hot air engine had no flat surfaces and was
a thin aluminium casting ,using an adjustable angle plate
the top surface is covered with some aluminium tape ,the part is
attached to the plate using some plastic padding ,it is essential to
put some release agent on to the casting to release the part
easily ,a single clamp through the central slot in the angle plate
provides enough clamping force to hold the part for machining
as the plastic padding in this instance forms a shoe for the
part to sit in.
Used this method many times for these sort of jobs, works
every time.

John

For those of you who wish to there is a petition to
oppose this proposed drone and model aircraft
registration here at

https://petition.parliament.uk/petitions/259863

Please take some time to fill it in and pass this on.

John

Before embarking on air mist coolant systems it may be worth reading this,

https://airfiltration.mann-hummel.com/fileadmin/user_upload/air_
knowledge/Air_Quality/Oil_mist_and_PM1/AA89_PM1_White_Paper_EN_v1.pdf

whilst this is primarily aimed at industry having such a system under your nose
whilst machining may not be the smartest thing to do.
I use neat cutting oils and in one application involves neat cutting oil applied to high speed
spindles,i know from previous encounter some years ago it turns instantly to fog,
as of yet i have not decided on how to combat this.

John

Posted by Duncan Webster 06/06/2019 12:57:16

Thanks John, Warco deny ever having made a GH1000 lathe, so could you just confirm it's centre height,
it looks similar to mine at 5". Looking forward to reading your articles in MEW, at least it is giving me a
handle on stepper motor size.

Hi Duncan,

Here are the original leaflets from 1999 as you can see the GH 1000 swings 13 3/8 inch over the
bedway and 18 1/2 in the gap.The stepper motor that drives the 10 tpi lead screw came from
Arc euro and was 350 Ncm 10 mm shaft 3.36 volt 4.2 amp /phase. As i use Compucut
an early hobby cnc system that is unipolar the output of the motor is slightly less but still
more than enough to do the job.
I see from the pages of lathes .co .uk that the Myford 254 has a protusion where the lead screw
passes through the rear mounting much like the Super 7 lathe.
I have a super 7 lathe that is also part cnc and is driven this way ,the problems in using the original
lead screw is the continual movement and wear of a cnc system as this is always going to be up the chuck
end and also the backlash in the halfnut on the machine,on a gearbox machine such as my GH 1000
there is also the additional drag of driving this around.

John

Edited By John Pace on 06/06/2019 18:33:57

The Z axis stepper motor drives the quill on the machine ,only a small
stepper motor was used have no details on this as it was a scrap box
part.The motor was mounted to keep within the profile of the head so
the head can still be if needed tilted 90 deg without fouling.
The lead screw seen here fits in place of the drill depth stop screw
and nut assembly which was useless item anyway,the nut has some anti
backlash adjustments.
The original block for the drill stop is replaced by a T shaped part that
has a horizontal dovetail and fixes to the quill using the same 2 holes,
a split clamp slides apart on the dovetail,when required for cnc operation
the clamp is positioned around the nut and secured with 2 m4 screws.
Two more photo's first one showing the underside of the table powerdrive,
i made a bracket to fit this to the end of the table and included a geared
take off ,a clutch can disengage the drive from the lead screw so the power
take off can be used with or without the lead screw engaged.View above
the gear output from the drive,one of those things done a long time ago
that was never taken to completion ,the cnc operations make this redundant
now.

John

Hi Duncan,

I converted my Warco GH 1000 to part cnc use and did not use
the original lead screw that is on the machine,i made a new lead screw
that has the stepper motor fixed on a bracket that clamps to the bed
of the lathe , it appeared in an article in mew in issues 207 through to 212.
No real alterations were needed to the machine i think i had to drill and tap
about 5 holes.
Even has it's own thread on here ,not worth reading as there is nothing
constructive in it.

John

Just some more photo's of the A2F,with the table right down there is
plenty of daylight under the drill bit ,the raising block is about 4 1/2 inches.
When i converted the machine to part cnc i made some new lead screws
and adjustable backlash nuts and gained a little more table travel to
21 3/4 inch and just over 8 1/4 on the y axis. The original machine nuts
are quite poorly made and fixed .The stepper motors came from Arc Euro
trade triple stack 34's 14 mm shaft 5 volt 6.5 Nm ,they don't sell these
now.The two photo's show the y axis motor tucked under the knee casting,
extending the hand wheel out it fouls the rise and fall handle on the left,the
hand wheel was moved to the right and drives the lead screw through a
pair of gears as i had made some lead screws i could use a right hand screw
for this .The stepper motor drives the lead screw via a toothed belt.
It is an imperial machine and the lead screws are 1/8 pitch the tooth
belt pulleys reduce this to .100 inch pitch.Photo of the x axis motor
both drive through 3/8 L size belts.The brackets are fabricated from
1/8 steel sheet .
With the table right up the two stage lead screw can be seen ,uses
the original lead screw with a fairly short extension piece the same pitch 1/8
inch about 1 1/2 diameter and a new nut fixed to the base.
Will post some more later on.

John

I have had one of these for 20 + years ,been a very good machine.Modified
mine to part cnc use ,raising block seen here in the photo allows
24 inches maximum spindle nose to table and a two part knee
leadscrew will bring the table up to the spindle nose.The raising block
has an unbroken tee slot and allows the the head to be swung around
as in this instance to mount an auxiliary spindle to cut a rack.
More info at lathes.co.uk look up EME millers.

John

Hi Andrew

Should have said pinking shears ,here they are ,one of the first
cnc type jobs that was done back in 2006 .The blades are
gauge plate hardened and only sharpened on the face ,there is
no clearance behind the cutting edge but they worked well enough
to cut the required tapes from paper.
The model Hurricane i think was started somewhere around 2004,
when i wrote the article in 2009 all of the main structure was completed.
The model was only finished last year such is the level of detail
of models of this type ,it has full cockpit detail and many other
features that would only be seen on the real thing.
David Knott the builder of the model has been British champion
many times and has been in the GB team several times representing this
country, maybe with this model he will win the world championship ,hope so.

John

An additional photo shows the set up for placing the fixtures down to
the mill table ,the dowel is held in the drill chuck and providing that the chuck
is not rotated during this procedure the fixings will be in the correct place
relative to each other.In Rod's case of the connecting rod it would obviously
be wise to check the alignment of the position of each fixture .

A little off topic with this part but for those of you who may have read the original article an opportunity to see the end result.

In the original article the subject matter was the production of a pair of
shears to make some dummy cover tapes for a model aircraft.
I am pleased to show here the model that was featured in the article
now completed with the owner David Knott in the centre of the
photo.He is the current British national scale model champion with
this model at last years national championship.

John

I use these simple fixtures for these sort of jobs seen in an article
in Mew January 2015 " Cnc fixings" .The pillar attached to the
slotted part is sacrificial can be made to any size and has a
hollow dowel and typically 4mm thread for fixing ,placing these
on the machine table can be part of the cnc cutting file ,i hold these
in a chuck and let the machine locate the position.The slotted part
must obviously be large enough to pick up the nearest tee slot.
The first photo shows four of these fixtures the second shows some
brass connecting links for a hot air engine being cut.

John.

On page 111 of the gear cutting book about three quarters down the first
column it explains the principle to get the blank roll.
For example to get a thirty tooth gear using your 72 :1 table
and using a 60 hole division plate= 72 x 60 = 4320 holes
for one complete revolution of the rotary table ,divide by
30 = 144 holes or 2 turns and 24 holes.
The blank roll would be 36 holes in the 60 plate.
The important point made in the book is that the dividing plate
must be able to be divided by 4.
You could of course if the plate is only divisible by 2 make
the cuts in the gear in 2 passes missing out the initial centre
gashing cut ,same page second column.

I see from your later posting that you have a 15 hole plate ,
the easiest solution is to use this and make a 60 hole plate
and from there the 20 tooth gear =72 x 60 = 4320 holes
for 1 revolution of the RT, divide by 20 = 216 holes or
3 turns and 36 holes ,the blank roll = 54 holes.
For the 40 tooth gear = 72 x 60 = 4320 holes for 1
revolution of the RT, divide by 40 =108 holes or
1 turn and 48 holes ,blank roll = 27 holes.

The sizes of the gears at the large end do not influence
these calculations ,trying to work out the rotation of the blank
roll in degrees will only lead to mistakes.

John