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Unread postAuthor: goathunter » Sat May 30, 2009 6:46 pm

http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=3448

Here's a starter kit, isn't the best quality but it does have the basic tools you'd need. I don't know about the ball cutter attachment though. Might have to build that yourself.
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Unread postAuthor: john bunsenburner » Sun May 31, 2009 5:12 am

Well I did say the tools I need to make the ball cutter, making it will be my first project, and will also help me with building my gun. Thats why I said that I need the tools to make it.
Looking at the link there is a load of stuff on there that I had no idea existed. Most probably I shoudl take a class or two at lathing or buy a book about it. Thanks for all the help, it was really useful, and I kind of have a picture of what things I need(ordering fro the US would be kinda mad so I have to find something similar here)
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Unread postAuthor: Technician1002 » Sun May 31, 2009 7:00 am

john bunsenburner wrote:Well I did say the tools I need to make the ball cutter, making it will be my first project, and will also help me with building my gun. Thats why I said that I need the tools to make it.
Looking at the link there is a load of stuff on there that I had no idea existed. Most probably I shoudl take a class or two at lathing or buy a book about it. Thanks for all the help, it was really useful, and I kind of have a picture of what things I need(ordering fro the US would be kinda mad so I have to find something similar here)


:D First since you have a lathe, the fist thing to learn, is it machining, not lathing. :D
A machinist uses a lathe and other machine shop tools.

From there lots of books are out for metal cutting, turning, and machining. Start with books. See if there is anyone nearby who would be willing to mentor you. Online is a fantastic resource. Use the free info first. Don't start with the ball cutter. You will waste material attempting an ambitious project right out of the gate. Pick up some scrap metal and get some cutting and measuring practice in first. Trying a complex project first will result in cursing the first time you overcut something and have to start again. (easily done. Cutting the front 0.1 inches deeper cuts the back 0.1 inches for a diameter change of 0.2. Mistakes come naturally at first.

Look online for recommended cutting speeds for various materials. Some math is involved. For example, a material should be cut at 60 inches per second and is 2 inches in diameter, what RPM do you use? You will need the circumference of the 2 inch round to get inches per turn (about 7) and find the RPM to get Inches per second. 600 RPM is 10 rev/sec or a speed of about 70 inches per second. 600 RPM would be close to the correct cutting speed. A 1 inch piece needs cut at higher RPM for the same cutting speed.

An online refrence to bookmark for cutting speed and feed rate is here.
http://littlemachineshop.com/Reference/CuttingSpeeds.php
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Unread postAuthor: john bunsenburner » Sun May 31, 2009 7:17 am

Thanks for that tech. Would you mind in that case having a look at my diagram of my gun's piston housing and telling me what parts of that I should make first? Or do you have a project recomendation that would make a good first project.
Also where would you recomend I look for scrap metal round bars or pieces there of. And whom should I ask about the mentoring.
Really I would like to get started on my gun as quickly as possible. So either i make it my first project(atleast parts of it) or I find a few other projects to do before attempting the gun. What do you think? Am I being too amibitous or just about realistic?
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Unread postAuthor: Technician1002 » Sun May 31, 2009 9:21 am

john bunsenburner wrote:Thanks for that tech. Would you mind in that case having a look at my diagram of my gun's piston housing and telling me what parts of that I should make first? Or do you have a project recomendation that would make a good first project.
Also where would you recomend I look for scrap metal round bars or pieces there of. And whom should I ask about the mentoring.
Really I would like to get started on my gun as quickly as possible. So either i make it my first project(atleast parts of it) or I find a few other projects to do before attempting the gun. What do you think? Am I being too amibitous or just about realistic?


For cheap scrap metal, visit a junkyard ( auto wrecking yard ) They try to sell replacement parts to shops. Don't fall for it. Tell them what you want. You don't need a 62 dodge axle. You are just looking for a round rod of some sort about an inch in diameter and up to bout a foot long. Mind if I look around and pick up some at scrap prices? Instead of a $60 dollar part, it becomes a $5 part. or less. Your rate may vary.

A good first project would be to make a flaring tool for tubing that would allow end to end splicing of copper tubing without a coupler. It is turned on round stock to fit into a copper tube part way, followed by a beveled edge to a new diameter that is the OD of the tube. When driven in, it expands the tube end.

It's simple and isn't a big loss if it fails and is useful if it comes out OK. No complex parts first. The bevel transition to the two sizes is the exercise. A bevel on the nose should be an obvious choice to make insertion easy.

Next a simple piston to fit an air cannon is the next logical choice.
A close fit that doesn't stick or leak much will teach tolerance and fit. Getting the right finish cut may take a few tries. It's easy to make lots of pistons too small. Goal is small enough to fit and slide freely, but large enough to have no noticible rattle. The piston will need to be only a couple thousandths small to do the job.
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Unread postAuthor: john bunsenburner » Sun May 31, 2009 9:54 am

Ok, that sounds like a good start but i don't work much with soft copper at all so a flaring tool is not really something useful for me, got any other ideas?
I do not know if you looked at my diagram but the piston has two O-ring grooves on it, do you think these could also be made as a second mini project or is that already too complicated?
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Unread postAuthor: Technician1002 » Sun May 31, 2009 10:57 am

john bunsenburner wrote:Ok, that sounds like a good start but i don't work much with soft copper at all so a flaring tool is not really something useful for me, got any other ideas?
I do not know if you looked at my diagram but the piston has two O-ring grooves on it, do you think these could also be made as a second mini project or is that already too complicated?


O ring'ed pistons are not too difficult. They make an excellent first or second project as there are no complex bevels, threads, or super critical dimensions. Some minor error are not a show stopper. Use your calipers to make all dimensions to spec. To face both ends, you will need to do one side and turn it around and finish the other side. See if you can do it without a joint showing where they meet. Get it so it is exactly the same diameter from end to end and there is no off center on one end. A lathe chuck with a tooth slightly imperfect (common) may cause the two turnings to not quite be on the same centerline. See how close you can turn a piece so they match from both ends.

I did look at the diagram. Are you planning on floating rings or do you want a tighter seal that won't burp when it changes directions?
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Unread postAuthor: john bunsenburner » Sun May 31, 2009 11:31 am

Well That is another thign I should ask:

I have calipers but they are manuel ones and accurate to the nearest mm, do you think I should get my self electronic ones? Also I think tigth O-rings would be better than floating ones in this gun, is there a difference in machining besides the obvious?
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Unread postAuthor: Technician1002 » Tue Jun 02, 2009 1:54 am

john bunsenburner wrote:Well That is another thign I should ask:

I have calipers but they are manuel ones and accurate to the nearest mm, do you think I should get my self electronic ones? Also I think tigth O-rings would be better than floating ones in this gun, is there a difference in machining besides the obvious?


A pair of Inside and Outside calipers (non measuring) should be part of any machinists toolbox. It is a quick way to check if the part is close to the right size and can be used where a digital won't fit while making passes to check progress.

Set them to the target diameter and use it while advancing cuts to check depth of each new pass. They can be used to quickly turn down a piece to get it near the finish pass without having to move the tailstock and carriage out of the way to use a traditional digital or analog measuring caliper. You can quickly tell when the diameter is almost the right size before making the finish pass.

Using the inside and outside ones together is an easy way to make a piston to fit a cylinder. Use the inside caliper to measure the cylinder. (no numbers, just set it to touch both sides on the inside) Once the inside caliper is set to this size, use the outside calipers to measure the inside caliper again just touching. Using the outside caliper, you can quickly turn down your stock to close to the proper size where the caliper just fits over the OD. When done the piston will be very close to a tight fit in the cylinder. Take a finish pass of a couple thousandths and it's done. No math and the piston is custom cut to fit the cylinder.
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Unread postAuthor: rp181 » Tue Jun 02, 2009 10:40 am

caliper's are great, you will find yourself using them all the time. My digital calliper's are more than 10 years old, but still looks like new, as it is a mitutoyo (or however that's spelled). Mine have a accuracy of .1mm, or .0005". Harbor freight also has cheap callipers.
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Unread postAuthor: jmccalip » Tue Jun 02, 2009 10:50 am

For a project like a piston valve, having super accurate calipers doesn't matter. You're simply comparing one measurement to another, as long as it gives you the same reading every time, that's all you need.


But Mitutoyo is a very good brand. That's all my boss uses, and he's had them for 5+ years, and they are still working perfectly. Just make sure you go with the dial kind. The problem with digital, is you never know if it's at "0". Sometimes they reset themselves, and you can mess up a whole batch of parts because you accidentally tapped the button and now your parts are off dimension. With a dial caliper, you can recheck it's accuracy by simply closing the caliper and see what it reads.

BTW, I believe the accuracy is as follows:

6" dial caliper = .001
8" dial caliper = .002
12" dial caliper = .002
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Unread postAuthor: Technician1002 » Tue Jun 02, 2009 12:22 pm

jmccalip wrote:For a project like a piston valve, having super accurate calipers doesn't matter. You're simply comparing one measurement to another, as long as it gives you the same reading every time, that's all you need.


But Mitutoyo is a very good brand. That's all my boss uses, and he's had them for 5+ years, and they are still working perfectly. Just make sure you go with the dial kind. The problem with digital, is you never know if it's at "0". Sometimes they reset themselves, and you can mess up a whole batch of parts because you accidentally tapped the button and now your parts are off dimension. With a dial caliper, you can recheck it's accuracy by simply closing the caliper and see what it reads.

BTW, I believe the accuracy is as follows:

6" dial caliper = .001
8" dial caliper = .002
12" dial caliper = .002


The problem with most measuring calipers are they don't measure diameter well from the side. For example my 4 inch digital caliper in front of me now. It opens fine to 4 inches. If I have a 3 inch diameter part in the lathe and am using the tailstock, there is no way to measure the piece simply because the jaws are only about 1 inch long. Try it. Block the ends of a 4 inch pipe and measure the diameter with the 6 inch dial caliper in the middle.

The only way to measure the 3 and 4 inch parts is across the end.

When making a 2 step piston, it is possible there is no way to reach the step from the middle or the end with a digital or dial caliper.

The machinists calipers will reach where the dial and digital won't. With the screw adjustment, they rarely get bumped when set down and picked back up.

The tips of my caliper are only 1.23 inches long. It won't measure a round part larger than 2.46 inches in the middle simply because it can't reach in that far.

This is typical of a digital caliper. Image
It simply won't reach across a large part from the side.


Edit, quick test.. Since you indicated you wish to make balls. Measure a 4 inch diameter ball with the 6 inch calipers. You will soon discover the advantage of having the other calipers. :D

Get the digital. You will love it. Get the other ones too to transfer sizes to what you are working on. I'm pretty sure your boss has both.

Note the reach of the inside calipers in my earlier post. They will reach into the cylinder of my Mouse Musket where the digital one won't. The digital caliper can't measure the size the piston needs to be.
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Mouse Musket with close fitting piston in the cylinder. A digital caliper won't reach inside far enough to measure the cylinder diameter.
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