Member postings for John P

Posted by Chris V 17/04/2021 18:21:50
I understand you put paper between the mill bed and lump you are milling to help stop slippage, do you also use paper between clamps and the job ie on the top face?

Chris.

You can do this if you wish ,i use these plate pieces to surround a job
clamped to the mill table ,they are nothing special just rough cut,  used with the normal clamping methods will hold a job securely in
place.
The part in the previous photo had bolt holes on the underside to fix to
the pair of angle plates.As this part was eventually ground on all four sides
it needed to be made and held in this way.

John

Edited By John Pace on 18/04/2021 10:13:54

Hi
The tee slot cut in this table is 250 grade cast iron it cuts very easily ,you
need to clamp the job down really well and lock all the unused axis ,when i
cut these i always leave about a 1/16 of an inch at the bottom of the slot
for the cutter to work against it takes a lot of the shock of the interrupted cut
away ,the cutter here is from Arc Euro 16mm dia 7mm deep ,obviously the
start needs to be at full depth.If you can the sharp edges of the cutter should be
chamfered to avoid a sharp corner in cast iron, about 1/2 mm is enough.
Power feed and a vacuum cleaner if you have it.

John

Hi William

Nice find that grinder ,they seem to be quite rare .it is almost made as a mirror image of the J&S 520 grinder ,i saw the photos in your album some time ago in the photo No4 the lettering on the casting looked as if it was JS0 by the drain hole at the rear of the machine but the machine did not look like the 520 grinder ,looks as if it is mostly there the end covers are missing from the table , certainly looks to be a Crystal lake grinder.I think that they are still in business .

Write some more when you get it going.

John

It was the similar type machine ,look on Lathes uk Jones and Shipman 520 cylindrical grinder. Is the machine

that you have in your album a J&S 520 grinder.

John

Crystal lake cylindrical grinder drive unit or similar type machine.

John

Hi Martin

Seeing what you have written it would seem that you may be grinding a full size
cam perhaps not for model size engines ,your smallish grinding wheel would be
about my normal size wheel 6 to 7 inch where the difference in size for a cam
blank of about 1/2 inch shows little error from a radius to a straight line.

For the model engine enthusiast these two videos from Sherline may be of
interest. Certainly for me , on seeing these my early attempts i was trying to run
the work perhaps too fast ,the attraction of doing these with cnc is there is little
more to make if you already have a machine as i have.

https://youtu.be/RrpdJHTPXFI
https://youtu.be/PffRGZjagBs

Perhaps you will write again about your cam grinding as it progresses most
probably in its own new thread ,i am sure it will be of great interest.

John

Posted by Oily Rag 09/04/2021 14:39:35

I am considering building a CNC cam grinder. This would involve either a stepper driven leadscrew for positioning the saddle longitudinally along the
bedway and a ball screw driven by a stepper for the cross slide. The cam would then be formed by controlling the relative position of the cross slide
to the rotation of the headstock spindle (by use of an encoder). The encoder would need absolute positioning capability so would likely have to be
something like a 4k 'greyscale' type.

My concern is would the reaction time of the cross slide be sufficient to accurately grind the cam form given that the peak acceleration/deceleration
rate of a cam can be in the region of 0.006" per degree. The ideal speed of the cam for grinding would be around 300 rpm to allow a small enough
grinding wheel (running at close to 4,500 rpm) to fit into the space needed. this gives a time per degree of 0.00055 secs which equates to a cross
slide speed of nearly 11" per second or 54.5 ft per minute.Can the control systems, both software and hardware, handle these type of positional
reaction speeds?

I realise that 'professional' systems are capable of these sort of speeds but are the 'hobby' systems capable likewise? Any comments and
suggestions would be most welcome.

As an additional note the reason for building the cam grinder is that I have a 'spare' bed and headstock and saddle that can be modified - It's too
good to scrap and it seems a worthwhile project to make some use of it rather than leave it to 'rust in peace'

Martin

Hi Martin
First of all the speed that you indicated seems a little high,
in this video

https://youtu.be/7vz-Z6x5ZLw

the cam is rotating at between 30 to 40 rpm that alone
would solve some of the points that you have raised.

As part of a project that i have still on going i have looked in to
grinding similar forms ,the photo here shows the machine set up here
with the stepper motor drive controlling the rotation of the camshaft axis
( the shaft fitted here is for something else not a cam)
at 1800 steps per rev, the crosslide moves 0.00005 inch per step.
I wrote a small file to simulate a camshaft but found like you , the
speed as the grinding wheel goes over the peak of the cam the
speed can be too high ,as part of the sequence the rotation speed
of the cam is incrementally reduced and increased as the grinding
wheel rises up and falls over the cam lobe ,i never got to the point
of cutting metal but some of the things that are gained just by these
simulations are of value.

The other thing to think about is at some point during the grinding if you
are using the encoder and crosslide to follow the cam shape
the crosslide will need to move independently to increase the cut depth,
unlike using these systems for threading the grinding is more of a
continuous sequence.

The rocking action of the cam being ground in the video almost
seems like the easiest solution and use the cnc part to make the
master cam.

John

Hi Chris

Looked at the linked site seems to be a complete package to do what you wish.
I suppose the real problems is fitting it to the Warco WM 280 lathe ,the Emco
from the 2nd poster Hubertus Fischer is much the
same as a changwheel Myford 7 lathe where direct access to the leadscrew is
possible ,with the Warco the leadscrew is connected though the gearbox.
I fitted a cnc system to my GH 1000 warco lathe and faced similar problems
it was featured as an article in MEW 207 to 212 i got around the leadscrew/gearbox
by fitting a removable second leadscrew ,the whole conversion only needed the
fitting of about 5 additional screw holes and still retained the full manual machine
operation.
There was some criticism about the article in this thread

https://www.model-engineer.co.uk/forums/postings.asp?th=88623

mostly by people who had not bothered to read the article properly ,one even
claimed that i had some complicated , " the gears, helical planetary ones" ,
of which there were none.

It would be worth looking at the mechanical connections needed before
committing yourself to proceeding with this type of conversion.

John

Hi

Don't know if these videos from "Find Hansen" have
come up before on here ,worth a look ,this one here
shows the operation of the diesel injectors .

https://www.youtube.com/watch?v=xh0Vzq6_C2s

John

Hi Michael

Have a look at this gear calculator from Ondrives it only works in module inputs so for 20 DP you would have to input 1.27 mod the interesting thing is when the checkboxes are filled in and calculated the diagram at the bottom of the page changes and shows the the tooth profile.

https://www.mesys.ch/calc/ondrives.fcgi

John

The list in my previous post was slightly corrupted when copying over to
posting.This may be a little clearer.

Dimensions for 1 DP 20 deg PA for other pitches divide by the dp.

20 dp 12 tooth .36/20 =.018" 12 tooth / 20 dp= pitch dia = .600 inch + .018 + addendum .100 inch
blank size .718 .This gives the minimum size with no undercut ,you can of course go larger but this
will eventually produce thin tops to the gears that will require " topping".

Teeth Correction

17           = .26
16           = .28
15           = .30
14           = .32
13           = .34
12           = .36
11           = .38
10           = .40
9             = .42
8             = .44
7             = .46
6             = .48

The same basic rule applies ,for module gear the correction is the tooth number x the
correction eg for a 6 tooth gear of 1 module 1x.48 =.48 added to the pcd of
6 mm = 6.48 mm + the addendum of 2 mm OD = 8.48 mm this is the minimum
blank size to avoid undercutting when hobbing a gear.

There are 3 examples here 1 mod gears . 1 cut at nominal pcd 6mm ,2 at 6.48 mm pcd
and 3rd cut on a 10 mm od ,the first one looks in the photo a little wonky it is the angle
of the camera ,you can clearly see the undercut ,the difference by adding the .48 mm
to the pcd can be easily seen, the last one just shows what happens when the blank
is taken to the maximum .All of these gears will mesh with each other.

Howard's suggestion that the caliper was not zeroed properly is not well thought
out , for if the caliper was not zeroed properly it would only read under size,i would have thought
most shed men would know this.

Getting back to the OP's original question he could use any size from the from the .723 inch measured by
AStroud to the machinery's handbook size of .762 inch ,the only other consideration is the distance
from the root of the tooth to the bore of the hub ,the recommended minimum in a book that i have
is circular pitch divided by 2 would be .078 inch ,my own Myford gear measures at .066 for this
dimension.

Thanks Pete for posting that copy of table 8 .I never had any information on these corrections
for 14.5 PA gears.

John

Edited By John Pace on 19/03/2021 17:58:39

Edited By John Pace on 19/03/2021 17:59:17

Edited By John Pace on 19/03/2021 17:59:55

Difficult to know why the difference in measured size of this 12 tooth gear,
in the following post to mine AStroud measured at .723.
As you can see here mine was .746 inch i bought this gear off the Myford
stand at the ME exhibition in the 80's the bore is .375 inch and the
cluster is case hardened.There may be a difference the super 7 and ML7 as
my S7 has a 30 tooth gear and is is 20 deg PA ,the 12 tooth gear will
be 14 1/2 deg PA as is the Myford change wheels .
In any event the limiting factor on the od is the width of the tops of the teeth
if the blank is too large the tops will come to a sharp point ,the gears will still run
but the tops will be weak.

Some useful info here if you are hobbing gears of 20 deg PA.
If you are hobbing the undercut can be left as it is ,to improve the strength of the
tooth at sizes of gears of 20 PA 17 tooth and below the corrections below
produce gears with no undercut.

In practical terms 5 teeth would be about the minimum and that would generally be
cut direct on a shaft as there is little material available to bore a hole in the middle,
eg Align power drive unit for milling machines.

A little more freedom with this is if helical gears are cut as the divide by cos helix angle
increases the gear diameter.

Dimensions for 1 DP for other pitches divide by the dp

eg
20 dp 12 tooth .36/20 =.018" 12 tooth / 20 dp= pitch dia = .600 inch + .018 + addendum .100 inch
blank size .718 .This gives the minimum size with no undercut ,you can of course go larger but this
will eventually produce thin tops to the gears that will require " topping".

TEETH

17 .26
16 .28
15 .30
14 .32
13 .34
----------
12 .36
-------------
11 .38
10 .40
9 .42
8 .44
7 .46
6 .48

John

Hi

The blank od for the 12 tooth gear that you have asked about is .746 inch in diameter.

John

Hi

You could try Dos box ,it seems as if it may be available for windows 10

it works on win7.

John

Hi Darren

I've found the page on the December 2020 Advantage for these micrometers.They are listed in the main book on page 871 as part no SPU 14346 K , as you may see there is difference in price than the listing on the Advantage page as part no UESPU 14346 K , they re-appear regularly in the advantage leaflet from time to time.

As far as the quality  aspect   i can't  fault them   as i have nothing else  to compare them with  ,as they follow  on  in size range  from one to the other  they are within   .002  mm  using the ring gauge   to check  ,that is within the specification  as  advised .  

John

Edited By John Pace on 01/03/2021 12:05:09

Hi Darren

The Micrometers came from MSC J&L They usually appear in the monthly Advantage catalogue ,they are not in this months catalogue March.

They are useful as you say to be able to measure where you are and eventually get to the size you need ,i doubt you will find a similar instrument within this price range .

John

Hi
I've woken up now and taken a photo of these micrometers ,of course they
only read to 1 um ,made by Spi not as good quality as Mitutoyo but they
are plenty good enough for use in the workshop ,as far as i can remember
they worked out at about £105 each they do sell them individually but
work out more expensive this way as the setting rings are not supplied.
The smallest here will measure into a depth of about 16 mm.

John

Edited By John Pace on 01/03/2021 09:48:19

Hi

Chronos have a dial bore gauge in their Dasqua range that measures between 4 to 6 mm ,not cheap at about £165 and also 6 to 10 mm at around £70 ,sometimes MSC J&L have sets of three point micrometers in the Advantage cat that range between 3.5 to 6.5 in 4 micrometers with setting rings even more expensive but measure down to .001 um .Not in this months catalogue.

John

Hi

Get a 24 gauge hypodermic needle has a bore of
.31 mm and an od of .55 mm which would be much
easier to drill and solder in to make the jet.

John

Hi

Have done a trial posting on the RCME new site , very easy to do photo went straight in don't know if it is in an album .Still prefer the layout of this forum as it is .

John