Author Topic: Chester 626 mill CNC Conversion  (Read 213066 times)

Offline David Jupp

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Re: Chester 626 mill CNC Conversion
« Reply #325 on: July 08, 2012, 03:28:32 PM »
If commercially produced, the 'rules' are independent of material - it's the Pressure Equipment Directive that would apply, classification is based purely on Fluid Type, Max Working Pressure and Contained Volume.  PED specifically mentions 'Permanent Jointing' in its Essential Safety Requirements - this is usually interpreted as Welding, but would (almost certainly) include Silver Soldering.

By its very nature, Silver Soldering shouldn't lead to any nasty deterioration of materials properties of Copper - Inappropriate welding procedures in Steel can leave problems with heat affected zones or embrittled material.  Silver Soldering of Copper therefore probably doesn't need such tight controls (It is hard to imagine a brittle failure of a copper boiler).

Steam generators are especially hazardous, so have their own classification chart in PED. 

I believe that a document was drawn up some years ago in consultation with the HSE as a Model Engineer's / Society's 'sensible guide' to how to comply with the spirit of PED, but avoiding too much bureaucracy.  I have no idea of the current status of such a document.  [EDIT - here is a link to a 2004 version of said document http://www.alanstepney.info/HSE.pdf , it refers to a mix of PED and PSSR.  It does require a 'competent welder' but gives no guidance on what that might be.   Edit ends ]

I do some work for companies that have to comply with PED - the whole system is quite a pain for any 'one off' even when there isn't any 'permanent jointing' involved.

Rob.Wilson

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Re: Chester 626 mill CNC Conversion
« Reply #326 on: July 08, 2012, 04:44:10 PM »
Thanks David

Very interesting document , so going by what is written i can weld up my own boiler ,all  the plans specify are  the material and to be welded by a competent person.   

I wonder if the document still stands .


Silver solder joints can be  overheated and can also have a lack of penetration  ,leading to a bad joint . overheating the copper can also have an adverse affect on the copper too .


Rob

Offline David Jupp

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Re: Chester 626 mill CNC Conversion
« Reply #327 on: July 09, 2012, 03:48:34 AM »
'Competent Person' also required for silver soldering of copper.    The interesting point is defining/demonstrating competence.

Copper/Silver Solder has far less potential for catastrophic brittle failure than steel.  Failure still possible but likely to be less dramatic than is possible with steel.

Does anyone know of an updated version of the document I linked to ?

Offline Jasonb

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Re: Chester 626 mill CNC Conversion
« Reply #328 on: July 09, 2012, 03:18:34 PM »
The "Blue book" would be the best document in the UK and the Australian codes are very good, they have one each for Copper, steel and Duplex boilers.

Also mention of test welds here
http://www.16mm.org.uk/newsite/insurance/Examinaton_Testing_of_Boilers_Nov_2008.pdf

The two things that worry me about your boiler are the fact you have ground down the welds and all those dummy stays. On all the steel boilers I've seen the welds are left as is and any dummy rivits added to the hornplates or false throatplate never into the actual boiler.

J

Rob.Wilson

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Re: Chester 626 mill CNC Conversion
« Reply #329 on: July 09, 2012, 06:41:33 PM »

The two things that worry me about your boiler are the fact you have ground down the welds and all those dummy stays. On all the steel boilers I've seen the welds are left as is and any dummy rivits added to the hornplates or false throatplate never into the actual boiler.

J

You presumed wrong about the stays Jason ,dummy stays what never , screw through both plates  and riveted on the outside , welded in the fire box .As the drawings states.
 
 
Dose it not look more like it should do with the weld on the back head  ground and riveted,  more authentic ?


Rob

Edit ,,, and the material used is 2mm thicker than required .

Offline David Jupp

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Re: Chester 626 mill CNC Conversion
« Reply #330 on: July 10, 2012, 02:12:05 AM »
Photos like that from throughout construction should be very helpful to show the inspector stuff that you can't see now (e.g. weld preps).

Offline BillTodd

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Re: Chester 626 mill CNC Conversion
« Reply #331 on: July 10, 2012, 06:30:23 AM »
Photos like that from throughout construction should be very helpful to show the inspector stuff that you can't see now (e.g. weld preps).

Photo's of Rob's workmanship generally are more than enough to convince me that the boiler is sound (not that I know anything about boilers)

He doesn't appear to bodge anything :)
Bill

Offline Ned Ludd

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Re: Chester 626 mill CNC Conversion
« Reply #332 on: July 10, 2012, 09:55:50 AM »
Hi Guys,
The aim is to get away from any Blue book or model engineering activities and join the real world, where the is an element of sense left, just. A real world boiler cert is just as valid as a model one.

Do you have to, in fact, claim "new build" can't you just let the tester assume it is old and let him do his ultra sonic thickness tests and hydraulic, then steam tests?
Ned
I know enough to do what I do, but the more I know the more I can do!

Leafy suburbs of NW London

Offline DICKEYBIRD

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Re: Chester 626 mill CNC Conversion
« Reply #333 on: July 10, 2012, 10:34:34 AM »
I think this thread should get an award for the widest gap of discussion subject matter.

All the way from hi-tech computer machine control to steam boiler construction. Yay!!  :clap: :clap: :clap:

Now, back to the mill conversion! :)
Milton in Tennesee

"Accuracy is the sum total of your compensating mistakes."

Rob.Wilson

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Re: Chester 626 mill CNC Conversion and other stuff
« Reply #334 on: July 10, 2012, 11:02:38 AM »
Hi David ,, yes i do have a few photos (ye oldey type film ) of the weld prep and route welds etc , i must get round to the scanning  them  into the computer.

Thank you Bill .


Hi Ned ,I could give it ago , but i will have a dig around and see what other info i can finned first .   


 :lol: :lol: :lol:  Dickey ,,,,,,, this thread dose ramble a bit  :Doh:


Rob

Offline arnoldb

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Re: Chester 626 mill CNC Conversion
« Reply #335 on: July 10, 2012, 01:54:08 PM »
Quote
yes i do have a few photos (ye oldey type film )
I bet everything will still be nice and shiny - even in sepia  :D :D

 :whip: :whip: Come on mate, back to work on the mill - seeing as you're doing such a grand job of it   :clap: :clap:

 :beer:, Arnold

Rob.Wilson

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Re: Chester 626 mill CNC Conversion
« Reply #336 on: July 10, 2012, 02:11:46 PM »
Hi Arnold  :lol: :lol: :lol: :lol: wonder were i can get my Daguerreotype processed  :scratch:

Cheers mate , i am working on it , resisting all other temptations , well nearly all    :palm:


Rob 

Offline 9fingers

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Re: Chester 626 mill CNC Conversion
« Reply #337 on: July 11, 2012, 04:56:14 PM »
Hi Rob,

Newbie here. Excellent thread. I have a Mford version of this machine and plan to convert it.
A couple of questions.
Are you going to replace the Z axis screw with a ball screw?
Are you going to counter balance the weight of the knee ie with a gas spring?

TIA

Bob

Rob.Wilson

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Re: Chester 626 mill CNC Conversion
« Reply #338 on: July 11, 2012, 05:53:47 PM »
Hi And Welcome too Madmodder Bob  :thumbup:

Yes i am replacing the  Z axis screw with a 25mm 5mm Pitch ball screw  , i am using a 12Nm motor 2:1  reduction . Allot more power than i need , so there should be no need to counter balance the  knee  IF i have my sums correct  :palm:

Rob

Offline 9fingers

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Re: Chester 626 mill CNC Conversion
« Reply #339 on: July 12, 2012, 06:28:10 AM »
Thanks for the welcome & replies Rob.

I noted you were using 12Nm motors. As part of my initial experimentation into steppers and drivers, I fitted a 3Nm motor to the existing X feedscrew with 1:1 drive as a power feed and that is just adequate.
With the lower friction of ball screws and 12Nm  I reckon you will have loads-a-power for X & Y.
I'm envious of your workshop facilities. I'll be trying to do my conversion with only a ML7RB (plus angle grinder :lol:) for any machine ops that I forget to do before disabling the Myford VMC.
Based on the shortage of space that you experienced with 25mm screws/nuts, I think I might use 20mm x 4 or 5mm screws.
The machine will only be for hobby use so I hope this will be adequate.

Did you get everything from Zapp? Would you use them again especially thinking of poor documentation with some items?


Apologies for all the Q's - I'll try and keep them to the minimum but there seem to be few write-ups on conversions of this machine.

My area of expertise is in induction motors so if I can return the favour anytime, feel free to ask.
http://homepage.ntlworld.com/bob.minchin/Induction%20motors%20-%20Issue2.pdf

Bob


Rob.Wilson

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Re: Chester 626 mill CNC Conversion
« Reply #340 on: July 12, 2012, 01:47:38 PM »
Hi Bob

Now that is a very well written motor document ,lots of info , i can see it coming in hand on phase two of the CNC conversion , when i change /mod the head of the machine . Thanks for sharing .  :med:

no problem about the questions , fire away i will try my best to answer them .

Being lazy i did do a one stop shop at Zapp ,, bought the motors,drivers ,PSU,BOB, pendant,screws,  and nuts from them , at the time they were the cheapest for most of the kit , I found there service to be spot on , everything was VERY well packed and they were very willing to help with any queries i had over the phone .Looks like there not too far away from you .

As to the documentation i cant really fault it , Driver manual and BOB manuals are great , yes the pendant info  is a tad iffy, but not hard to work out .

The belts ,pulleys,bearings i am just getting local .

20mm screws will be fine for the XY , but things will still be tight ,there is not allot of difference in the nut size , thats why i went for the largest i could get in , also there is less force required to move a 25x5 screw than a 20x5 screw , there is loads of room for 25mm or larger on the Z .

I hope take the time to share your CNC conversion with us here  :poke:

Rob




Offline 9fingers

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Re: Chester 626 mill CNC Conversion
« Reply #341 on: July 12, 2012, 02:48:27 PM »
Hi Rob,

Thanks for your kind words.

I think that the standard you have set during your conversion will be soooo much better than what I will achieve but yes I will do a write up from time to time in a separate thread. I've been taking a few work in progress photos already.

I have just added a 1200N adjustable gas spring on the Z axis and have now balanced the table with a vice fitted and a few blocks of steel to represent a workpiece.
I had previously estimated the weight of the knee to be about 100kg (bathroom scales under the Z nut  :bugeye:)
It felt very strange to put more effort in to lower the table than raise it before letting some gas out from the spring.
I now need about 6Nm torque to move it either up or down using the standard feedscrew and the helical gear drive.
I am just about to order a 12Nm motor and a 2:1 ish belt drive. I realise the motor rating is the holding torque rather than the driving torque. If it is not man enough, I can put in a ballscrew instead or apply the drive direct to the screw to loose the gearing losses.

Zapp do seem to carry just about everything I'll need and as you say they are nearby if I do need to visit.

Cheers

Bob

Rob.Wilson

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Re: Chester 626 mill CNC Conversion
« Reply #342 on: July 13, 2012, 06:02:59 PM »
Hi Bob

Any chance of a photo or two  of your gas spring set up ?

Drew up the X,Y motor mounts 



The Y axis motor mount  will be 30mm longer  between centres so the motor can clear the underside of the  knee casting .I was going to make them both the same as the Y axis  ,but the X looked naff with the longer mount


Rob ,,,,,,,,,,,,,,,,,,,and JS no they will not be blue LOL 

Offline micktoon

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Re: Chester 626 mill CNC Conversion
« Reply #343 on: July 13, 2012, 06:25:32 PM »
Looking good as usual Rob, how long would it take you to draw out something like that ? is it quite quick once you know what you are doing ? I look forward to seeing them getting machined . Cheers Mick.

Offline doubleboost

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Re: Chester 626 mill CNC Conversion
« Reply #344 on: July 14, 2012, 06:34:57 AM »
Very nice drawings Rob  :thumbup: :thumbup: :thumbup:
I would have thought you would have made them a bit more "shiney like"
John

Offline 9fingers

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Re: Chester 626 mill CNC Conversion
« Reply #345 on: July 14, 2012, 08:24:28 AM »
Hi Bob

Any chance of a photo or two  of your gas spring set up ?

 

I've started a new thread Rob so as not to clutter yours.

http://madmodder.net/index.php?topic=7345.0

Bob

Rob.Wilson

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Re: Chester 626 mill CNC Conversion
« Reply #346 on: July 14, 2012, 05:03:02 PM »
Hi Mick ,I actually have no idea how long it took to draw  :palm:  i just do a bit here and there . :smart:


Made a start on the motor mounts today , slow start , the closest stock i had to hand was a length  of  4"x1" so I copped a couple of lengths off to make the mounts from .


Drilled and counter bored a couple of holes in a part of the job that will be machined away later so i could bolt the work down ,

 I was going to mill the thickness of the bar down ,BUT my four inch HZ slab mill needs a sharpen  :palm: ,So i opted to bolt them to the lathe face plate for machining .




Now the job could be mounted on the mill to machine the width and length to size , I used two ring parallels (made up name LOL)  actually two inner bearing races ,true precision tools from scrap  :med:


Mounting the work like this means i could machine all round the part in one go ,making all the edges parallel and square .


Rob


Offline John Stevenson

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Re: Chester 626 mill CNC Conversion
« Reply #347 on: July 14, 2012, 05:14:06 PM »



Mounting the work like this means i could machine all round the part in one go ,making all the edges parallel and square .


Rob

And do the chrome plate all at one go...............................................................

Where's that freeking Ju-ju doll ?     Pass me that big bodkin needle...........................

John S.
John Stevenson

Offline doubleboost

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Re: Chester 626 mill CNC Conversion
« Reply #348 on: July 14, 2012, 05:57:25 PM »



Mounting the work like this means i could machine all round the part in one go ,making all the edges parallel and square .


Rob

And do the chrome plate all at one go...............................................................

Where's that freeking Ju-ju doll ?     Pass me that big bodkin needle...........................

John S.

Looking at that lump of" scaly shite being "transformed in to chrome plate has me feeling quite sickly
John

Offline krv3000

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Re: Chester 626 mill CNC Conversion
« Reply #349 on: July 14, 2012, 06:37:15 PM »
lol