Member postings for John Pace

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

Posted by Neil Wyatt 14/03/2019 22:09:51

Good idea John, a bargain basement (<£5) angle grinder 36-tooth
gear might be just the thing for a small rotary table.

Hi Neil,

Not so sure how that a mating worm could be made to work
satisfactory with one of these gears.
The principle of these spiroid gears is the form of the hob is
the same as the worm that is used to drive it.

The photo here shows the gear being cut ,this gear was made
using prototyping wax as it was just an experimental tryout.
A proper gear would need a hob to be made similar to the
style in Heartland gears www.itwheartland.com.As can be seen
the thread form is asymmetric.

The position of the centre distance of the hob needs to be
noted down as the worm has to be placed in this exact position
for this to work.
At 60 tooth and 1 module a spur gear would be 62 mm od ,
this spiral gear also 60 tooth is 84 mm od.
As worm and wheel rotary tables have the worm outside the radius
of the wheel the case size is larger than it needs to be to accommodate
this.
As the placement of the spiroid worm is within the radius of the gear
a larger gear could fit within the same size casing of a rotary table.
As far as accuracy is concerned i can't see that it would be any
different to any other generated gear form.
John

I just wonder how long rotary tables will be made in the conventional way .
Other threads on rotary tables have highlighted the strength problems
with worm and wheels .
This video shows these spiroid and helicron gears which can be made
with zero backlash.
https://www.youtube.com/watch?v=gRriAf5snqs

A photo here of a test gear hobbed using a 1 module cutter ,the worm would
fit in about the 1 o'clock position and have about 5 teeth in mesh at the same
time.
John

Myford .8 module change wheel set and Warco Gh 1000 1 module change wheels ,both keep within the machine covers.

John

Here is a drive unit that i made ,toothed belts work fine for these and don't leave a chatter pattern on the work and provide a positive drive.Three speed gearbox and variable speed motor gives a drive speed from 20 to about 700 rpm.

John

Hi Maurice,

I you have ever used some silicone sealant the tapered nozzle that is on the tube always has some left over sealant inside that sets inside , pull it out and you have a tapered plug of silicone ,cut it as required to form a suitable silicone cork.

John

A 4th axis is an essential accessory and opens up what is possible to do.The compressor wheel on the left is milled from 2014 t6 aluminium 68 mm in diameter ,the one on the right is a bought cast wheel 66 mm dia for a KJ 66 model gas turbine.

John

Edited By John Pace on 04/03/2019 09:38:33

Double posting.

John

Edited By John Pace on 25/02/2019 09:55:36

Rocol Tufgear universal open gear grease is a sticky grease that retains it's position when applied ,RS sell it part no 388 8465 may be cheaper elsewhere .Good for changewheels etc very messy.

John

Some photos of a geared oil pump for a machine coolant
system.The gears are 1.25 module driven by a 12 volt
dc motor of about 20 watt ,pumps about 2.5 litre minute at zero
pressure through 2 filters to remove micron size particles
from the system.
The smaller gears are from various fuel delivery pumps for a
model gas turbine ,the middle size gears pump about 1 litre a
minute at about 40 psi,end leakage on the small gears is more
of a problem as they are only .050 inch wide and need
careful fitting.

John

The Quorn in it's basic form is unable to sharpen milling cutters
along the flutes with any great success along with many other
hobby type cutter grinders that use the same type of setup.

The problems are all the same the friction of the workhead and also
the guide rest in the flute of the cutter.
Even when attempting to do this there is a size limitation that
makes this impossible to do even if you were to have an air bearing
work holder.
In the first 20 years i had the Quorn i don't suppose that i tried to
sharpen along the flutes more than a dozen cutters, most of them
were not much better than before i started.

In the time since then i made this cnc grinder which uses the Quorn
head, up to now i have sharpened hundreds of cutters along the flutes
from 2,5 mm dia to 20 mm dia all of the cutters that i use, they
all come out as sharp as new cutters and in some cases sharper than
new cutters from some suppliers.
The resolution of the machine is 1/20 th of a degree and as such the
clearance angles can be set with this sort of accuracy.

John

Posted by John McNamara 7/01/2019 13:23:07

Hi John Pace.

GMTA I made the same toolbit using the carbide shank from a
PCB drill, PCB drills are so tiny to hold up they are made from
very fine grain carbide. Tough too.

I milled a piece of key steel of the correct size and silver
soldered in place. Been using it for a couple of years. The ten
degree angle you normally use for the Diamond tool can be reduced
to around 5 deg by angling the template. More robust for heavier work.
However it will work fine as standard.

Regards
John

Hi John,

I don't use the supplied fixture to sharpen the toolbits,some while ago
I bought 10 off 1/4 square toolbits from J&l supplies they were on offer
at about 80p each 10% cobalt.
Both ends are sharpened as can be seen in the photo .I had this process
scribbled out on a piece of paper and have tidied if up here for use
on the Quorn grinder or tool grinders with similar axis. This may be useful
for others wishing to do this.The self centering 2 inch four jaw chuck is
from Chronos and makes this much easier to do.

Having 20 ground ends if one is dulled it goes in the grind box and
a fresh one fitted.

The carbide tips that are ground similar to a CCMT shape only need regrinding
on the top until the are worn down enough that the sides need doing again.
Grinding the carbide is best done towards the cutting edge to avoid chipping.
These days the tangental toolholder gets the most use.

John

I silver soldered this 1/8 inch carbide shank into a suitable size square piece,the edge is milled out about half the diameter and the piece soldered in ,it seems to work best if left as a round shank.The round piece fits neatly between the clamp.

The one on the left is ground to conform the the square shank ,because carbide chips easily when ground to the acute angles of the diamond tool a shallower angle is needed at the top and both the sides need a little grinding for clearance.

Useful for harder materials and maybe cast iron.

John

I built one of these sandblast cabinets 20 + years ago from
a kit of hardware parts and the drawings for the cabinet
made from plywood,it will run all day on the same size
of compressor.

It looks as if the vent on the back of the bin blaster has a
filter in it these are worse than useless as they block up very
quickly so the dust finds the next easy route out.I doubt
that it would be wise to use this inside the workshop you
would find out why the next time you use your lathe.

My own cabinet is sealed and vented externally.

Rubber gloves 24 inch in length are avalable from J&L
Pt no GLV-90082E.

John

Posted by ega 14/01/2019 10:58:45

In the introduction to his 1997 book Harprit Sandhu invites corrections.
I wonder whether it would be possible for him to be invited to comment?

I bought the book partly because, having faced the challenge of building
the Quorn spindle I was interested in knowing if there were easier ways
to achieve the desired result.

Edited By ega on 14/01/2019 10:59:05

I too have built a Quorn spindle and with care they run well ,it must have done
as i have had it 30 years and it has never been apart.

The photo shows 3 grinding spindles under construction,based on the layout
of the Quorn type spindles with modifications.

The outer sleeve is bored through for a close fit for the bearings,in this way
the bearings will be in line axially.

The shaft is made with bearing seats this gets rid of the bearing spacer tube
and makes the shaft much stronger as it is larger in diameter in the central
portion.

The two sleeves seen in the photo, the shorter one is eventually loctited into
the outer sleeve in the correct position ,the longer sleeve forms the spring box
to push on the rear bearing much the same as the Quorn design.The spacing
of the bearing seats on the shaft is a few thousanth's more than the total
length of the two sleeves limiting the amount of axial movement.

The two screwed end caps similar to the Quorn ,the front one traps the
outer raceway ,the rear cap is clear of the bearing.
In this way a nut fixing is required at both ends of the shaft to trap
the inner raceways to the shaft, as these form part of the labyrinth
seals these are much easier to do.

Perhaps the biggest advantage of constructing in this way is that all
of the turnings are single operations and require no turnarounds for all
of the important features.
The bearings are SKF C3 Eco 17x 35 mm bearings rated for 25,000 rpm
and are more than good enough for the expected loads,i expect that
angular contact bearings a better bet if the spindles were to be used
for milling.

John

I had a similar problem with my Warco lathe .I made an add on plate the full length of the crosslide just over an inch thick ,it is held with six 6mm cap head bolts ,holes for mounting parts are drilled as needed.If your lathe is similar to mine about the rear third of the crosslide is little more than a cast in cover and is quite thin in section so careful placement of the bolts is required.

The topslide mounting ring will most likely be too far from the centre line of the machine to be of any use in holding work in any event to fit longer tee bolts you will probably have to remove the crosslide.

John