Here is a list of all the postings Martin Connelly has made in our forums. Click on a thread name to jump to the thread.
|Thread: Stainless steel boilers|
The designation of sch40 or sch40s depends on which ANSI standard is being applied. ANSI B36.10 does not use the s after 40 but ANSI B36.19 does. since at 2" there is no dimensional difference it does not matter if you put the s in or not. #
The issues of stress corrosion and stress cracking possibly apply more to a model boiler than to industrial applications. An industrial application may only have a few pressure or heat cycles a year, a model sized boiler may have more in one day than an industrial application. The smaller boiler may also locally heat up and cool down faster and since stainless has lower thermal conductivity than copper and less ductility this cycling could be more damaging.
Welding stainless without backing gas on both sides of the weld to keep oxygen away would result in a weld that was highly contaminated with oxides. As mentioned in a post by Brian Dickinson in 2012 you need to purge the inside with an inert gas, usually argon, to make satisfactory welds in stainless steels. MIG welds also tend to produce unacceptable sharp changes in section that act as stress raisers and can also cover up all sorts of poor preparation and internal shrinkage cracking. A TIG weld in stainless made by a good welder is a thing of beauty and looks like it has been made by a machine.
For pressure vessels you need a full penetration weld to avoid stress raisers. With TIG you can create a weld pool and hold it in position until it has had a chance to go all the way through with closed butt welds before moving around the joint, you can't do this with MIG. With open butt welds you have to do something similar but form a bridging weld pool that is then continued around the joint . For anything over 1mm wall thickness we used to form a weld preparation by bevelling the edges so that we could get this full penetration weld then had to have multiple passes and a capping pass. The time to produce this weld preparation and subsequent weld in something like 2" NB sch 40 pipe was about 1 hour. We would not have wasted time on it if we could have just MIG welded them and produced a satisfactory job.
Edited By Martin Connelly on 27/01/2022 13:52:21
|Thread: Small MT2 Tailstock Chuck for ML7|
Get a pin chuck and mount it in the standard chuck. Do not tighten the main chuck down enough to stop it from moving. You can restrain the pin chuck with your fingers for these small drills and move the pin chuck into the workpiece by hand giving a good feel for the cutting action. You may need to add a collar to the pin chuck for drills that are bigger than your Ø0.25mm ones.
Edited By Martin Connelly on 27/01/2022 13:32:07
|Thread: Stainless steel boilers|
One of the things that came out of the nuclear industry's use of stainless steel for hot pressurised fluids was that austenitic stainless steels, such as the 300 series, could suffer from intergranular corrosion if there was any chloride in the fluid. As a result they had a requirement of (IIRC) less than 30ppm in any fluid that was used, even when hydrostatic pressure testing before being put into use. This could cause issues for places with hard water that may have dissolved chloride salts, including common salt NaCl, causing internal structural damage that could only be detected over time with x-ray or ultrasonic NDT. The biggest issue for the pipes made from 321 or 316 stainless steels where I worked was in the highly stressed and thin corrugated bellows of flexible pipework. The pressure testing water could gather in the bellows and deposit chlorides in them that was hard to remove. Since the town water was very hard and also contained a lot of iron we used a water treatment system to remove almost all the impurities with RO for pressure testing purposes. We later found the NDT department were using untreated hot water on the pipes as part of their colour contrast crack detection. We had to write a new process specification for them to ensure they also followed the no-chloride rules.
William, the Hemingway's machinists hammer handle is a long and slender tapered part and Guy said he was machining it between centres, I presumed with the tailstock centre offset. There are a number of variables that could have changed but using a basic carbide tool for this seems likely to be a simple thing to change to HSS and see if it improves the machining. Trying to find a good rpm or speed for a tapered part will not be easy since the diameter is constantly changing.
|Thread: Smart TV|
Brian G, just a bit of information that may interest you. I was reading about the early history of insulated wires in a paper by Allan A Mills. He studied pieces of wire from the early days of electrical experimentation by people like Faraday and Ritchie. He was able to get hold of a few samples off some pieces of apparatus held by various museums. What he found was that since molten copper readily absorbed oxygen most of the wire they used had a very nice outside sheath but that the core was full of oxygen rich bubbles where the oxygen had come out of solution as the copper solidified. This increased the expected resistance by about 15%. This problem of oxygen in the copper was not sorted out until the 20th century when electro-refining started to be used and copper billets were melted and drawn under a blanket of inert gas.
As a result of modern manufacturing methods I think just about all modern copper wire will be oxygen free and people selling cables at a premium because they are oxygen free are making extra profit from other people's lack of knowledge on the subject.
It would be useful to know what inputs the smart TV has before going any further with suggestions.
Carbide inserts are made from a powder that is pressed into shaped then heated to bond the particles together (sintering) and are generally not sharpened after that process. This leaves a slightly blunt cutting edge. They also have a nose radius typically 0.2mm or 0.4mm for the small sizes used on hobby lathes. Part of this bluntness is needed since a sharp piece of carbide can be very brittle and will snap off if poorly handled at any point in its journey from manufacture to first use. The **GT inserts Jason refers to above are ground and polished to be sharp and have a profile designed for aluminium so are much more suited to the less industrial machines found in many home workshops. They work well on other materials as well including stainless steel and HSS.
What you can do with HSS is form the cutting edge with a simple grinder then use a suitable fine stone finish the edge really sharp and to put on a radius that is far smaller than the 0.2mm that is likely on the inserts you have. There are plenty of YouTube videos on this. I have seen some people saying they can sharpen their HSS tools to the point they could shave with them.
The other thing that can be done with HSS is a vertical shear tool. There have been a few threads mentioning these, they can make very fine cuts if made and used correctly. The last discussion was in October 2020.Shear tool
For a long slender part one solution would be a travelling steady however that will not work on a tapered part. I would suggest trying HSS as you can get it much sharper than carbide inserts.
|Thread: skip find box of slot drills|
You can use threaded shanks in ER collets and finger collets gripping the parallel shank with no problem. I have never used the holders with a screw designed for shanks with a flat so can't comment on how well that works but I think I would avoid that set-up. Since they are likely to be 3 sizes of metric (Ø10, 12, 16) or three sizes imperial (3/8", 1/2", 5/8" ) only if you get a square ER collet block and a few collets that match the threaded shanks you can hold them securely in a 4 jaw chuck and ensure they are running true as well.
Edited for unwanted smiley
Edited By Martin Connelly on 24/01/2022 12:41:57
|Thread: The future of casting kits|
Bill, I started thinking about the costing of the two process options, cast v CNC. I quickly decided I could never get enough information as it really does need insider knowledge from a company that is doing the work. I used to write Applications for Capital Expenditure (ACE) when we wanted to purchase machinery. This had to state the problem that needed solving, what the proposed solutions were, how much they would save, the payback period and there were expected to be at least three options considered in the solutions. If you couldn't make a case on paper then there was no way you would be allowed the funds. In order to write the ACE you needed to know a lot about the company cost rates, how much cost they put on floor space, what services were available, the ongoing consumable, service and maintenance costs etc. All sorts of things you would only get to know if you were heavily involved with the people who could tell you these things. Some of them did get a bit imaginative with the costings but as they had to go in front of a list of people they had to be at the very least plausible. Some of them took well over a year to go from start, thinking of what needed to be done, to finish, first use and validation.
|Thread: DIY tool holder for inserts|
|Thread: Smart meter|
Surely if the error was an incorrect meter serial number then the smart meter that was cut off would have been your daughter's neighbour's. That would have caused even more trouble for BG
|Thread: Mach3 control loosing zero|
Setups are in the XML files. I and others in Mach3 groups have had corrupted files that had to be re-installed due to weird happenings.
Make a copy of your .XML and .DAT files into a new folder, rename the Mach3 folder something like "Mach3 old" and reinstall Mach3. Then copy the .XML and .DAT files into the new install. Sometimes Mach3 files get corrupted and cause all sorts of odd things to happen and this is the easiest way to rule this out. If it makes no difference you still have the original Mach3 folder to go back to if necessary.
|Thread: The Curious Case of the Cracked Injector|
We used to do a part at work that had two autogenous welds in Ø32 x 1.2mm wall 321 stainless steel. The central part had to be made 2mm longer than nominal to allow for the weld shrinkage that occurred due to the two welds. We regularly had to re-melt welds to pull parts back to square after welding. Elbows in pipes were the biggest cause of this as they had a thicker inside wall due to being bent when made. The forces involved with trying to prevent the movement were very large. I am not surprised they were high enough to cause cracking in a relatively brittle material. We were always having a go at the people who put out drawings with tight tolerances on welded parts, pointing out that if they wanted such exact sizes then the part needed machining after welding and stress relieving. I have seen a 35mm thick plate bend after welding was carried out on one side only.
|Thread: Crossfeed inaccurate|
If it is due to a bent shaft as suggested above then the notchiness would likely appear at the same point in the rotation of the leadscrew, so is this the case? If you plot the actual movement versus expected movement on a graph is it cyclical or random? At one end, centre or other end of the leadscrew?
|Thread: Smart meter|
I've had two dates to fit a smart meter. No one turned up for either of them but I did get a £30 credit each time as it was their failure to appear. I couldn't mind a few more appointments like that.
I've also seen news reports that before they get smart meters installed everywhere they will have to start modifying or replacing all the ones that have been fitted already as the signals they use are scheduled to be turned off by 2030.
|Thread: Lathe change gears vs gearbox|
The first thing you need is a list of the thread TPI or pitches you will need to cut and find out if it rules out any of your options. It should make it easier to narrow down the best option for you if there are some threads that can only be done with a lathe and some lathes can't do them.
|Thread: Crossfeed inaccurate|
As above, if tightening up the thrust bearings causes jerkiness then back off the nut until it is smooth again. The issue with older lathes is that there will be uneven wear of the leadscrew. The tool movement per turn of the handwheel will vary depending on where you are on it. The two ends tend to be nearly as new but in the middle it will be worn. This wear is magnified on a lathe as it doubles when the diameter is checked. The simplest solution is to approach the desired size then measure what you have and adjust the next cut to suit. Repeat until the desired diameter is achieved. The other issue is that any difference in centre height of the part to the tool tip will cause a difference between the target diameter and the actual diameter. This is hardly noticeable with large diameters but becomes a problem as the diameter gets very small.
The final thing is how sharp is the tool? You cannot remove 0.001" (I'm using inches because you said it was an old Colchester) with a blunt tool, it will rub. Trying a second cut by putting on a further 0.001" may still rub. The third attempt may start cutting but will now take off 0.003". This gives the appearance of jerky movements.
Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!
You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.
Click THIS LINK for full contact details.
For subscription issues please see THIS LINK.