N&W S1a Project - Tender Build

Where users can chronicle their builds. Start one thread and continue to add on to it.

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gamh44
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Re: N&W S1a Project - Tender Build

Post by gamh44 » Sat Nov 24, 2018 3:20 pm

Not too bad - just a little slow. I did have a false start as I did not account for the 0.4mm channel in the second bend, which added a few unnecessary holes.

bobrauper
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Re: N&W S1a Project - Tender Build

Post by bobrauper » Fri Dec 21, 2018 10:06 am

Hello Geof,
I have to say that your truck bending jig is Genius! The flexibility that it offers to form radius's and curves is second to none. It is the ability to add simple follower blocks and forming curves that make this design outstanding! Thank-you for showing that detail to us. I will remember this design and may make one just to have it on hand. It's really clever.... I an interested in seeing how you put the truck together and will be watching your postings. Keep up the good work!
Bob Rauperstrauch

gamh44
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Re: N&W S1a Project - Tender Build

Post by gamh44 » Tue Dec 25, 2018 6:17 am

Thanks, Bob. Very kind of you to say.

Almost done with the jig. The very last bend ended up being a little short so will need to rectify that before getting into mass (4) production. Frames will be brazed together - not sure if I will go silver or bronze at this stage. I am thinking silver as it should flow into the joint, hopefully leaving just a small fillet on the outside. I'll do (at least) one test before getting stuck in.

Geof

gamh44
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Re: N&W S1a Project - Tender Build

Post by gamh44 » Sun Dec 30, 2018 6:55 am

As above, I need to make a small adjustment to the bending jig to finish it all off, then onto mass production. So that has been set aside for a bit while the wheels are attacked. I picked up some discs from a (not so) local supplier and have managed to finish off one wheel - see photos below.

Turns out the discs are an absolute pain to machine. Initial thought was that just the mill scale was hard but it is most of the way through - just a little better towards the centre. Cuts are a maximum of 0.002". Beyond that, the HSS tools are dulled and require sharpening. Good news is that there is plenty of practice for grinding HSS tool bits. I have read (somewhere) about heating and slow cooling to help soften mild steel. I might give this a go for the next one.

Any suggestions on how to do this or other ways to speed up this process are most welcome.

I also made the mistake of ordering about 5/16" oversize so there is plenty to remove!

Here are the first cuts.
49. Wheel1.JPG
Almost done on the front side.
50. Wheel2.JPG
Fixed to an arbour, finishing the inside.
51. Wheel3.JPG
All done.
52. Wheel4.JPG

Harold_V
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Re: N&W S1a Project - Tender Build

Post by Harold_V » Sun Dec 30, 2018 5:01 pm

gamh44 wrote:
Sun Dec 30, 2018 6:55 am
Cuts are a maximum of 0.002". Beyond that, the HSS tools are dulled and require sharpening.
Speaking from the position of a guy who has used HSS for more than 50 years, that doesn't make sense. It's common knowledge that light cuts are harder on a tool (for wear) than a reasonable depth of cut. You should explore other possibilities, assuming your lathe is capable of taking a healthy cut. Large material on a small lathe can be troublesome, as they often lack the required power and rigidity. If you can detail exactly what problem you've encountered, could be there's a solution. Scratching away at stock removal @ .002" isn't an acceptable substitute for roughing.
I have read (somewhere) about heating and slow cooling to help soften mild steel. I might give this a go for the next one.
Depends on a few things. Lets start with the idea that you're working with mild steel. That means it has low carbon content, and is not subject to heat treat. If it is truly mild steel, heating the piece (annealing) shouldn't make a significant difference. If it does, then it's not mild steel. You can heat mild steel to a critical temperature and plunge it in water to quench and you shouldn't be able to detect a change in hardness.

If the pieces you have have been torch cut, it's possible that the slag and cut line are hard. In that case, annealing will be quite helpful.

A tip.

Cutting scale is really hard on cutting tools. You can expect a short life on any tool when it is used for that purpose. The best way to avoid it is to take a deep cut, so the scale is removed well behind the tip of the tool. You might even experience wear at that point, and that will be the cause of tool failure, but the tip will remain sharp.
I also made the mistake of ordering about 5/16" oversize so there is plenty to remove!
Using negative rake carbide and adequate power and rigidity, that's just one pass with course feed (.012" per rev., or more). That amount of stock can be removed for one wheel in less than a minute when you have the proper setup. It can be on a lathe that has a three horse motor, maybe even two horse. If you run a smaller motor, you should still be able to do it with a couple passes and a little more time. It all depends on your lathe.
I am a staunch supporter of the use of HSS, but there are times when one benefits greatly by the use of carbide, especially negative rake. It is mandatory that you have the power and rigidity to support its use, though. Make sure you can run fast enough and the machine will tolerate the required cut. If not, it won't be of benefit. In such a case, you're better off using HSS---but you must understand how to rough. Taking repeated shallow cuts is not the way.
Be happy to talk about it if you wish, assuming you don't have the idea how to go about the process. Be advised, you must understand chip breakers in order to do this successfully.

Edited to add a comment. The last picture shows some beautiful workmanship. Very nicely done!

H
Wise people talk because they have something to say. Fools talk because they have to say something.

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Fender
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Re: N&W S1a Project - Tender Build

Post by Fender » Sun Dec 30, 2018 5:36 pm

If the wheels were torch-cut, then removing the hardened edge with a grinder may speed things up, so the first cut in the lathe is softer stuff. What speed are you turning the wheels? When taking a heavy cut with hss, I get better results with a surface speed about 100 feet per minute or less, and liberal use of cutting oil.
Dan Watson

gamh44
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Re: N&W S1a Project - Tender Build

Post by gamh44 » Mon Dec 31, 2018 3:37 pm

Harold and Dan

Thanks so much for your detailed replies.

Here are some factors that I see contributing to the problem.

A. machining experience
B. tool grinding capabilities
C. lathe size - power and rigidity (it is a relatively small lathe)
D. material selection.

Before I started on the real wheel, I thought it might be a good idea to see how I went turning a prototype. I selected some steel that I had in stock and machined up a complete mock up about 90% the size I needed (I couldn’t find any bigger material floating around at the time). Here is the result (sorry, only photo I have on hand).
19. Bogie B.JPG
I cut a fresh HSS tool to do this and didn’t need to sharpen it for the whole wheel. Light cuts, heavy cuts, fast and slow feeds - no problem. Compared to the real wheel, it was like a hot knife through butter.

So while A, B and C above would definitely be factors, my initial thoughts are to do with the material - hence the annealing question.

So about the material. The steel in question was ordered as mild steel. It is not torch cut and has what I suspect is mill scale on the circumference. The first cut I made was to remove this - indeed with a deep enough cut to get through it. This is where everything started to go pear shaped. After a few attempts and adjusting speeds and feeds, I decided to machine the face. This has been already cut so I thought hardness shouldn’t be an issue. It was better but only marginally. Closer to the centre *appeared* to be softer. I thought this could be to do with a slower speed so dropped the RPM but that made no difference. There is no speed info on the lathe so I used a tacho app on my phone and I am running well over Dan's 100fpm recommendation so I'll need to look at that.

Harold, A quick search of the interwebs on chip breakers yields a load of results - the very first one is your post on this forum back in 2007, as well as a few others. A very interesting read and I will be doing some testing on this material shortly. If I can improve on A, B and C above, maybe D will not be such an issue.

In a recent tidy up in the workshop, some previously hidden suitable material was found - enough to do five maybe six of the eight wheels. I will have a go at this but will still need to make one or two from the same material as above. Your tool grinding tips will be a fantastic resource for this.

Thanks again for your valuable input.

Geof

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Fender
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Re: N&W S1a Project - Tender Build

Post by Fender » Mon Dec 31, 2018 5:29 pm

If there is a big difference between your "test" wheel and the steel you ordered, I suspect the problem is that you're not dealing with mild steel, but something else. Don't know if annealing will help, but here's a discussion on annealing cast iron wheels:
viewtopic.php?f=8&t=107572&p=401913&hil ... ng#p401913
Dan Watson

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Re: N&W S1a Project - Tender Build

Post by Harold_V » Mon Dec 31, 2018 5:34 pm

gamh44 wrote:
Mon Dec 31, 2018 3:37 pm
So about the material. The steel in question was ordered as mild steel. It is not torch cut and has what I suspect is mill scale on the circumference. The first cut I made was to remove this - indeed with a deep enough cut to get through it. This is where everything started to go pear shaped. After a few attempts and adjusting speeds and feeds, I decided to machine the face. This has been already cut so I thought hardness shouldn’t be an issue. It was better but only marginally. Closer to the centre *appeared* to be softer.
That comment may be key to the problem.
I thought this could be to do with a slower speed so dropped the RPM but that made no difference. There is no speed info on the lathe so I used a tacho app on my phone and I am running well over Dan's 100fpm recommendation so I'll need to look at that.
If my hunch is correct, yeah, you were running too fast.

While you may have ordered mild steel, they may have sent something else. It's been known to happen. Many of the alloys are rolled hot, so they have scale. Hot rolled mild steel shouldn't present any of the problems you've mentioned, but if you had the misfortune to get something else, speed would be a deal killer with HSS.

Did you experience any tearing in the cut? The finished wheel is quite pretty---as if the material is harder than mild steel, which tears badly in the cut, and leaves a far less pretty finish.
Your tool grinding tips will be a fantastic resource for this.
I'm going to assume that you understand chip breakers, and what to do if they don't perform to your expectation.
There's two ways you can remove material. One of them is with negative rake carbide, which requires a very rigid machine and excessive horsepower, due to the speed of the spindle. The other is low spindle speed, deep cuts, often lighter feed rates, and proper tool configuration. In your case, with a light duty machine, you really don't have the first option. You might be surprised how well the second one works, though. Grind your tool with a broad and deep chip breaker, ensuring that you achieve respectable positive rake at the cutting edge. Be mindful that the chip should flow nicely, so don't grind an abrupt edge in the breaker. A nice, gentle radius is preferred, which encourages the chip to flow. Use a moderate feed rate, and slow you spindle to no more than 75 sfpm, assuming you can. If your tool is properly ground, you can take a deep cut, with the chips yielding either a coil, or broken 9's. Because of the slow spindle speed, you won't burn the tool, and you'll be able to remove the stock with far fewer passes. Good practice dictates that the entire wheel should be roughed before you do any finishing, although you may not be able to do that for all features. Do as many as you can, including roughing the hole, before you start finishing cuts.

I'm short of time right now, so if you would like more information on the tool geometry, please make mention and I'll try to post a picture of a tool that would suffice.

H
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Fender
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Re: N&W S1a Project - Tender Build

Post by Fender » Mon Dec 31, 2018 5:44 pm

One other thought, if the photos are indicative of your turning setup, there may be excessive overhang with the tool bit. You want a minimum of the bit sticking out of the turret tool holder, and the tool to be as close to the center of the carriage as possible, not hanging to one side. With the arbor setup, rigidity will be much improved if the right end is supported by a center in the tailstock.
Dan Watson

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Re: N&W S1a Project - Tender Build

Post by Harold_V » Tue Jan 01, 2019 1:09 am

Yep! I agree. I'd also choke up on the mandrel, gripping it as close to the chuck as is possible. Keep things close, and gibs snug, but free. Goes a long way towards better machining, with far fewer issues.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

gamh44
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Re: N&W S1a Project - Tender Build

Post by gamh44 » Tue Jan 01, 2019 2:01 pm

Dan and Harold

Thanks once again for sharing your experience. It looks like I am now back on track (pun fully intended) to machining these wheels up in a reasonable amount of time.

I dropped the spindle speed just one more pulley and things improved significantly. Cutting through the scale was done with a cut of around 0.020", with no degradation of the tool. I am not convinced that the material is not playing a part here but at least we are moving forward.

I am still using the same tools as before but will now grind up some new ones, paying closer attention to chip breaking, which will no doubt improve things further.

With the photos of the tooling, I tend to move the tool post away from the work for photographs. There is actually very little overhang of the tooling, with the exception of the boring bar, of course.

The arbour its a different story though. There are only a few very light cuts to do at this time but still, no reason it cannot be shortened and held closer to the chuck.

Appreciate your thoughts!

Regards


Geof

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