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Member postings for tractionengine42

Here is a list of all the postings tractionengine42 has made in our forums. Click on a thread name to jump to the thread.

Thread: Snifting valve
18/01/2012 12:32:02
Hi
May I ask how is it that a vacuum is created. From what I can gather when the regulator is shut off a vacuum can be created between the regulator valve and cylinders. Are the pistons, now not being fed with steam, pulling a vacuum?
 
Thanks
Nigel

Edited By tractionengine42 on 18/01/2012 12:32:45

Thread: What is EN24 like to machine?
14/01/2012 11:59:25
Hi Raymond
Other than in the annealed condition En24T is the easiest to machine in the range T to Z.
All the conditions T to Z are hardened, they are given different tempers to achive different mechanical properties, T condition has the highest temper and therefore the easiest in this range to machine
 
I have not heard of En 24 M,
 
I have used En8M which is great to machine but is a lower strength material.
 
Nigel
14/01/2012 00:37:56
Ian
 
For En 24 the added suffix indicates the material heat treated condition.
 
En24 'T' condition is hardened and tempered and quite tough to machine, in my experience it's a case of reduced speed, small depth of cut and adequate feedrate when using a light machine. Carbide tools are best, you can go to high speed very fine cuts and feeds for finishing however I find good finish is relatively easy to obtain at slower speeds and plenty cutting oil.
 
In 'T' condition Its tensile strength and hardness are in the range of grade 8.8 to 10.9 high tensile bolts. Most high tensile bolts will be either one of these grades, socket head cap screws are generaly of a higher 12.9 grade.
 
If you have been machining high tensile bolts then EN24T wil be similar.
 
En24 is commonly available in annealled conditon (M???) and heat treated 'T' condition.
 
As John S indicates, 'M' condition is easier to machine than high tensile grade 8.8/10.9 bolts.
 
Nigel

Edited By tractionengine42 on 14/01/2012 00:43:32

Thread: To CNC or not to CNC - that is the question.
13/01/2012 11:03:48
Hi John
I am only scratching the surface with what I am doing, there is lots of free and very cheap stuff.
For 2D I use Draftsight and Vectric 2D, John S gave details above.
 
For 3d like the valve body I currently have the luxury of autodesk inventor which is very expensive. However, there are many other options that I am sure others can advise on one being Alibre for 199 pounds. I have used this and its OK. This will allow you to create your 3D model which you save as an stl file format. Vectric do do a 3d post processor but I use Meshcam for which I paid around 90 pounds.
 
You create your model in 3d software (Alibre), save as stl and load this into the post processor (Meshcam) which gives you the g code which you then load into your cam software (I use mach3 from Artsoft) The valve body was about 30 minutes form starting the 3d model to loading gcode into mach3.
 
The 3D modelling software does have a bit of a learning curve but online tutorials are great. If you can dedicate some time you will crack it in a coupole of days. The post processors Vectric and meshcam are dead easy, by short learning curve.
 
There are many more options.
 
FYI
I am only using a small shirline mill I bought for 200 pounds on ebay. Adding the controller and stepper motors cost about another 300 pounds.
 
I am not using ball screws, on the Shirline you can adjust backlash to below 0.1mm which I find Ok even when down milling, it does leave a witness mark when the feed changes direction but as I do the final finishing by hand it no problem. (You can see the witness mark on the inside valve body as the Z axis has changed from down to up) I don't use milling cutters bigger than 6mm, mostly 4mm and smaller.
 
Nigel

Edited By tractionengine42 on 13/01/2012 11:07:08

13/01/2012 01:12:32
Just to concur with John S comment about learning G code.
 
Reference to my post above, each part was programmed in 5 to 10 minutes without any knowledege of G code. The post processors used were Vectric 2D and Meshcam. 30 minutes is enough to learn how to use these programmes and start producing G code for real parts.
 
Getting started was not without problems, this and other forums provided fantastic support.
 
 
Nigel
12/01/2012 18:45:53
Hi
I recently added a small cnc facility to my workshop, while I prefer conventional methods which are much more interesting and challenging the CNC adds some options for parts that I can't do other wise.
In this respect I limit my CNC to a) Parts that need engraving/etching b) parts that would otherwise be expensive or long delivey castings c) parts that would require alot of fabrication and silversoldering. Here are a few examples.
 
 
Above is a water lifter in 2 halves to be silver soldered together and finished by conventional machining and by hand. Left is one half finished on the inside only, on the right the matching half complete inside and out.
 

Above is a steam header just off the cnc and ready for conventional turning/drilling and finishing. This would otherwise be a casting or fabrication.
 

Above are brackets ready for hand finishing. Could be done by conventional machining but I think most modellers would prefer a casting.
 

Above is a name plate ready for finishing and infill painting. This would otherwise probably be a casting or maybe etched.
 
For me the cnc adds some conveinience and control over buying castings. While I can fabricate I don't like fabrication involving alot of parts, my preferance here would be to cnc what I can.
 
Nigel
PS sorry for any bad spelling, I wish this forum had a spell check.
 
Thread: 20/40 DP gear hob
24/12/2011 06:05:41
Spoke to soon
I found the answer here
 
It's not an involute gear hob but it is an involute spline hob. The spline is 20DP but has a shallow depth equivalent to 40DP.
 
So no good for cutting gears I presume.
 
Nigel.
24/12/2011 04:53:41
Hi
I was looking at gear hobs on ebay.
 
This one is described as 20/40 DP,
 
I know what 20 DP is and what 40DP is.
 
How can it be both 20/40 DP? Can anyone explain this description?
 
Cheers
 
Nigel
Thread: Girder crown stays - are they overstressed?
23/12/2011 13:43:15
I have read with interest Jason’s and Michael’s comments above, both making valid points.

I quick look at the Princes of Wales boiler does show some interesting differences.
 
While I agree that the P of W girder stays look more substantial there arrangement/connection to the fire box crown has differences that will change the loading condition and stress distribution. Another observation is the Prince of Wales boiler appears to have a flat fire box crown (albeit thicker) whereas the D& NY has a curved fire box crown.

There is no question about the integrity of the design but I think it’s interesting to learn more about these girder stay designs. Michael, if you could give me more boiler details I would be interested in doing some analysis. If you send me a PM I will give you my email address.

How much does cutouts in the girder stays help water circulation? How much do they improve steaming?
 
Nigel
Thread: Bearing Material
21/12/2011 00:50:13
Hi Alan
Cast Iron bearings with mild steel shafts is a very traditional combination, the graphite in cast iron helps provide lower friction. Cast Iron is also good when used with hardened steel shafts.
Cast iron will tend to 'glaze over' considerably reducing ware.
 
If you wanted to use bronze then leaded bronze is good with mild steel shafts and lower surface speeds as will be the case with your model. Many other bronzes are more suitable for use with higher surface speeds and hardened shafts such as phosphor bronze grades. Leaded bronze is very easy to machine, the lead content providing free machining qualities.
 
There would be little point in having a cast iron housing and fitting a bronze sleeve bearing, just stay with the cast iron on its own. Only if the housing is steel for example would you want to fit a cast iron or bronze bearing sleeve.
 
It won't apply here but FYI most bronzes are not suitable for high loads, the bronze can become deposited on the shaft due to the load, aluminium bronzes with hardened shafts are more suitable for heavy duty applications. Aluminium bronze is difficult to machine.
 
Nigel
 
 
Thread: Girder crown stays - are they overstressed?
20/12/2011 23:27:42
Hi Stub/Jason
I have subsequently included the cutouts in the girder and cross members. There is no change to the stress levels only some slight changes to the stress distribution as you would expect.
 
It's best to build up FEA in stages, then you learn more about the application and it makes it easier to resolve any FEA model problems.
 
Paul, this analysis is indeed a vindication of the original design work.
 
Seasons greetings and best wishes to everyone for 2013
 
Nigel
19/12/2011 12:50:16
I have had some email correspondence with Paul regarding his original post, “Are my boiler stays over stressed”.

To answer his question I carried out an FEA (Finite element analysis) based on the drawings of the Durham traction engine boiler by John Haining. The results are shown below.

The materials are all copper except for the boiler firebox side stays which are specified as bronze.

The analysis confirms that, for the copper crown stays, the stresses at an operating pressure of 90 psi range between 6 and 24 N/mm2 well within the design limit of 26 N/mm2. (3770 psi). This stress is much lower than the 113 N/mm2 (16400 psi) which Paul calculated correctly for a simply supported beam.

The bronze stays have a maximum stress around 50 N/mm2, again well within the material yield strength.
 



This analysis verifies the original designer provided a very sound design which has been demonstrated by the many examples in steam for many years.
 
Nigel

Edited By tractionengine42 on 19/12/2011 12:52:30

Thread: Morse Taper Removal
17/12/2011 03:20:22
Here is a simple solution by a Sherline owner.
 
It's cnc machined but can easily be modified for other machines and convensional manufacture. Does require the spindle to have some extension available though so, in this respect, may not be a universal solution.
 
 
 
Nigel

Edited By tractionengine42 on 17/12/2011 03:21:26

Thread: Girder crown stays - are they overstressed?
09/12/2011 00:51:43
Paul, if it interests you I can look to do some fea analysis, I will need a copy of your boiler drg. or sketches etc.
 
FEA does have limitations and results have to be viewed with such limitations in mind. Allot depends opon the users knowlede of the application and skill in preparing the simulation however, it will give a clearer picture. The analysis will be linear, that is it assumes all strain is elastic no account being takes of re-distribution of stress in areas of high stress concentration etc. This can distort results a little.
 
All I am saying is, it's not the be all and end all but can improve understanding of the application, in that context it can help identitify how and where to make improvements.
 
If you want to take this further send me a PM.
 
Nigel
Thread: Copies of Old Model Engineer magazines on disk?
27/11/2011 02:09:38
Here is a previous post re. ME on CD.
 
 
Nigel
My link does not seem to work, here is the URL: http://www.model-engineer.co.uk/forums/postings.asp?th=33408

Edited By tractionengine42 on 27/11/2011 02:11:11

Thread: Vectric 2DCut and Mach3
19/11/2011 12:29:19
Hi ian
I use autodesk inventor for my work so I am able to use this for creating quite a few dxf and stl files for my cnc work. This software allows you to fit text to a curve.
 
If I can help you with a particular requirement send me a PM and I will see what I can do.
 
Nigel
Thread: what does this mean on a drawing
15/11/2011 15:41:11
Here is a useful tolerance chart
hole tolerance
Thread: Scriber
14/10/2011 18:01:31
I have been using a 0.1mm dia x 10 deg carbide engraving cutter, it has half it's dia ground away like a 'D' bit making the point 0.05mm. I have found it provides a good line for locating a center punch and hard wearing, thay are very cheap on ebay, just bought some 5 for 5 pound + 3 pound p&p. They are advertised as PCB engraving cutters
 
Just to clarify, I am not engraving the line, I am using the engraving cutter as a scriber, The cutter is 1/8" dia, I drilled the end of a 3/8" bar and loctited it in.
Nigel

Edited By tractionengine42 on 14/10/2011 18:06:20

Thread: Vectric 2DCut and Mach3
12/10/2011 15:29:53
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Ha Ha.
You did get me, for a moment I thought it was "back to the CNC" or should that be drawing board
 
 

Edited By tractionengine42 on 12/10/2011 15:35:26

Edited By tractionengine42 on 12/10/2011 15:36:45

12/10/2011 14:14:25
Result

1st Vectric 2DCut engrave
2nd Vectric 2DCut - pocket mill
Allchin Front Wheel Hub
Milling cutter 0.2mm x 20 deg engraving cutter, 8000 rpm, 200mm/min max.
23500 lines of code.
A liitle more conventional machine work to do then just need to infill with red enamel and polish
 
 
Nigel
 

Edited By tractionengine42 on 12/10/2011 14:19:17

Edited By tractionengine42 on 12/10/2011 14:26:21

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