Need Help Designing Fire Piston Cylinder and Cap

[snakerun]

Hello everyone,

I am fairly new to the carvewright community and am currently limited to using the basic software. I need help creating a fire piston. Basically It is a 2 piece item 1 being the cylinder and 1 being the piston. I plan on using dowel rods for the piston so basically I need help designing the cylinder and maybe a cap that would allow a person to hold the piston and compress it without jamming a dowel rod into their palm. These items are for intended for long term survival in a wilderness setting and have been traditionally only made from wood. I have pretty much figured that the cylinder will have to be a 2 piece carve that is double sided however the basic software doesn't allow me to create the parts. The cylinder would have a 3/8" id and a 7/8" to 1" od. If I were to choose the shape of the cylinder I would make the od in the form of a hexagon so that the glue lines didn't show up and it would simply have a hole on the interior of 3/8" that would go almost to the bottom of the cylinder. So it would go maybe all but half inch of a 5" cylinder and would have a cap the thickness of the board and the same shape of the cylinder that I could glue the piston into so that I could use my palm to compress the piston into the cylinder. If anyone would be willing to help me design this project I would be willing to pay a modest amount for the design time.

[DickB]

Are you more interested in learning how to do this yourself with Designer Basic no add-ons, or would you rather have someone do it for you?

[Sliverfoot]

Never heard of one before. Interesting.

[Digitalwoodshop]

Didn't have a clue what a Fire Piston was... Pretty cool....

This would be a fun project for a Rotary Jig for the CW if you wanted to get fancy.


https://www.youtube.com/watch?v=jGyl8w16VbU

[snakerun]

Hey Dick,

Thanks for reaching out. I definitely would like to get a handle on these carve regions and how to set them up. I went through a learning curve with the software one time years ago and went away from the machine. Now that I am back to using the machine I feel like I am trying to learn a foreign language.

[DickB]

All,

snakerun and I spoke on the phone, and also through Facebook. snakerun said he would rather learn how to do this with Designer Basic, no software add-ons, than have someone provide a finished mpc. I'm willing to go ahead with a step-by-step in part to help snakerun, but also because I think that this might be useful to others in a more general sense. Yes, I know this can be done quicker and easier with software add-ons, but I am going to share some techniques that I learned before Designer Pro and the add-ons came to be. This may benefit other Designer Basic users.

I will start with the cylinder design. The piston will be a dowel with end cap as snakerun posted. The piston will sealed with a string gasket as proposed by snakerun, and I won't cover that detail. The cylinder will be a 2-piece design that will be glued up per snakerun's post. The exterior will be hexagon in shape again per snakerun.

This will be a step-by-step tutorial. I will provide instructions including screenshots but probably no mpcs - the idea is to follow along and do it yourself.

Comments are welcome, but let's keep them along the theme of a tutorial using Designer Basic only.

Dick

[DickB]

To begin, we're going to need a couple of patterns: one for the inner cylindrical bore, and one for the external hexagon shape.

All versions of Designer, including Basic, allow us to import a height map and make that into a pattern. What is a height map? A height map is a 2D graphic grayscale image, where black = highest and white = lowest. (I was a presenter at the 2015 Carvewright Conference, so I am borrowing a couple of slides from my presentation.) Here is an illustration of a height map on the left, and the resulting pattern on the right:

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It's noteworthy to point out that a height map is not a photo, and vice versa, although you may see some resemblance:

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We can use various drawing programs, including free ones, to draw height maps in 2D and convert them to 3D patterns. The 2D drawings will not make a lot of sense as pictures, but they will as height maps. Conversely, pictures that make sense to the eye typically do not make for good 3D carvings, as you can see by the picture of the hydrant and the resulting pattern.

I'm not going to go into any detail on how to make a 2D height map maps using drawing programs. There are numerous drawing programs and all have their own learning curve. I will provide some simple geometric shape height maps that we need for this project.

[snakerun]

What type of free drawing program is available for height maps. I am running linux on my laptop and windows 98 on my carvewright computer. In my defense the computer for the carvewright is the only windows computer in the house and it is only used for the carver. If I understood more about drawing height maps I might better know what type of program to use but I have never even heard of a height map drawing. Also at this point I have no graphical drawing experience.

[DickB]

What type of free drawing program is available for height maps. I am running linux on my laptop and windows 98 on my carvewright computer. In my defense the computer for the carvewright is the only windows computer in the house and it is only used for the carver. If I understood more about drawing height maps I might better know what type of program to use but I have never even heard of a height map drawing. Also at this point I have no graphical drawing experience.There are many. I use paint.net and Inkscape. I also used a tool called Wolfie's Gradient Designer, but I don't think the author makes it available any longer and I'm not sure that I should post it. I'm sure there are dozens more. Best to pick one and stick with it for a while, as there is a learning curve for each. You can find tutorials for each darwing program online.

Most any 2D drawing program can produce a height map. You just have to think black = high, gray = medium, white = low, and make a drawing with regions colored with the appropriate shade of gray corresponding to the desired height. (OK, sometimes I think black = low, white = high, but there is always the Invert tool!)

Take a look at this thread:
https://forum.carvewright.com/showthread.php?21789-Model-St-Paul-Union-Depot&highlight=union+depot


I used paint.net to basically color in the drawing that my acrichect friend gave me with shades of gray (and black and white) to establish various heights or depths of carve.

(You will not need the drawing programs for this project - I will provide a couple of simple height maps that are needed.)

[lesuer27]

Awesome DickB, looking forward to hearing the rest of this project!

[DickB]

Next step is to make a half-cylinder pattern.

Here is a height map of a half-cylinder:

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Download it to your computer (click on the thumbnail image to enlarge it, then right click and select Save Image As...) and put it somewhere handy. I have a folder for height maps.

Open Designer and click on File – Import – Import Image File. Under Source, click on From File. Browse to the half-cylinder height map and open it:

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Click on Next. Click on the red lock icon to unlock (blue). Set the width to 1, the depth to .5, and the length to 5:

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Deselect the Floor Edges checkbox. Click on Finish.

Pick a folder, or use the New Category button to make one. (I often create a category for a specific project.) Enter a name such as half cylinder and click Save.

Before we use this pattern, we need to cover the topics of Bit Optimization and Floor Feather. Those will come next.

Meantime, go through these steps. Play around with the options if you like to get familiar with them.

Extra credit: Google height map, click on Images, and find some grayscale graphics. (Careful – not everything that you see is a true height map!) Here is a good example:
http://www.gigamacro.com/blog/gigapixel-depthmaps-3d-data-export-case-study/


Make a pattern out of it. (Hint: for this particular pattern, click Invert, then click the down arrow under Raise/Lower to lower it a bit. What happens?)

And you thought that you had to pay money to get a penny pattern! You might be surprised at what interesting height maps you can find and convert into patterns with Designer Basic only.

[bergerud]

I have yet to make a fire piston. On my list. I cannot, however, see how the CW can carve the cylinder to anywhere near the precision required. Is there a plan to "hone" out the crude cylinder that the CW makes?

How about inserting a brass tube when gluing the two halves together?

[DickB]

Yes, we discussed making the cylinder slightly undersized and finishing with a 3/8" drill bit. You may recall I drill pilot holes in my clock gears with Carvewright and finish with a drill press to get the precision that I need.

I saw that some DIY instructors on the web use metal tubing. That would be an option, but this one is to be all wood.

[DickB]

By default, when carving a pattern the center of the bit will follow the contour of the pattern. I’ve used the 3/16” ballnose carving bit to emphasize the result with our half-cylinder pattern:

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While the tip of bit follows the pattern, because of the width of the bit the resulting carving is not a perfect semicircle like we want.

Fortunately there is a solution: Bit Optimization. With our pattern selected, click on Bit Optimization and select Best. Now the software will take into account the width of the tip of the bit, and carve the semicircle that we are looking for:

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In Designer Pro, there is a feature called Floor Feather. Without going into a lot of detail, this feature was implemented to make feathering more pleasing when the pattern’s periphery does not have a uniform depth. It forces the entire periphery of the pattern to be equal to the lowest part. This is nice in some cases, but for our pattern it is not. Here is an illustration of our pattern in Designer Pro with Floor Feather disabled (left) and enabled (right):

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We do not want to use Floor Feather! Unfortunately, in the latest version of Designer Basic, Floor Feather is always enabled, and there is no way to turn it off!

However, as it happens, when Bit Optimization is enabled for a pattern, it virtually eliminates the Floor Feather result. Not entirely – can you see the small “lip” at the edges of our half-cylinder in Designer Basic and in the resulting carving?

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This can be a problem in some cases. For us it is not going to be a problem, because we are going to carve our cylinder slightly undersized, then finish with a 3/8” drill bit. So this small defect will not matter.

Next, we will work on creating a pattern to make the hexagon-shaped outside of our cylinder.

[DickB]

To design the outside of the cylinder in a hexagon shape, we’re going to need two sloped sides, or wedges. Here is a height map for a wedge:

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Follow the same steps as you did for the half-cylinder to make this into a pattern. Set the depth to .75”, the width to .75”, and the length to 4”.

(BTW these dimensions are somewhat arbitrary, because we’re going to change them after we place the pattern on the project board. I like to generate patterns as large as or larger than necessary. My thinking is you get better resolution by shrinking a larger pattern than stretching a smaller one. I could be wrong. Also, these patterns can be used for a variety of projects by simply altering the dimensions, depth, and height.)

We’re going to make the two halves of the cylinder from ½” stock. I used an online right triangle calculator to compute the following dimensions:

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(bergerud is the mathematician, so if you have questions on how to do this he is your man!)

Finally, we are ready to start laying out our project!

[DickB]

Start by creating a new project board with dimensions 6” x 3” x .5”.

Use the Pattern Tool to select your wedge pattern and place it near the bottom of the board, below the board’s centerline. Click on Pierce. Center the wedge horizontally with the Center Horizontally tool. Do not change Bit Optimization for the wedges – leave it at None.

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(If you can’t find any of the tools to which I refer, you can add them using the View – Toolbars checkboxes and Customize, or just click on Tools to find them.)

Place the wedge exactly half the width of the top surface,.577/2 or .289”, away from the centerline. To do this, click on the green number at the centerline (your number is likely different from mine) and enter.289. The number should turn yellow, indicating that it is a constraint:

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In the toolbar under Size: , set the width of the wedge to .289 (the second number). Designer Pro lets you enter width and length numbers independently if you wish; Designer Basic preserves the original pattern’s aspect ratio, so you can’t change the length directly. But you can change it by dragging the edge of the pattern. Select the yellow dot to the right of the pattern and drag until the length is 5”. Zooming in on the dot will help with this. No worries if you can’t get it exact.

Change the feather from the default ½” to 1/8”. Mirror the pattern vertically with the Mirror Vertical tool:

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Draw a rectangle. Center it horizontally and vertically. Set the dimensions to 5” and .577”. Click on the Carve Region tool. Change the default depth from .250 to .001. (We actually want this to be zero, but Designer complains when you try to upload a zero-depth region to the card. It treats .001 the same as zero without complaining.)

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If you had done the above steps in Designer Pro, and unchecked Floor Feather on the wedge patterns, life would be good. Not so for us. Click on Rear View. What do you see? Our wedges are disconnected! This is Floor Feather rearing its ugly head. Fortunately, there is a work-around: making the top surface of our hexagon a bit wider than it should need to be. Go back to the front of the board and increase the width of the top rectangle slightly, and then go back to the rear to see if it has been fixed. Repeat as necessary. Make the width as small as possible while still fixing the problem.

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Next we’re going to clean up the pierced part of the carving by making the pierced region a bit larger. If this is not done, the pierced area could be very ragged, or not completely pierce at all. Draw a rectangle, center it horizontally and vertically, and set the dimensions to 5” x 1.25”. Click on Carve Region and then click Pierced. Set Feather to 1/8” and flip feather.

We could be done at this point, but notice that the carving bit is going to “cut” the ends of the wedges. That’s OK, but unnecessary. Because it is the tapered carving bit, the cut is not going to be square – we would need to square it off in a subsequent step. Also, we are carving more material at either end of the wedges than necessary.

We could simply eliminate feathering of the wedges and pierced rectangle, but it turns out that feathering is actually less hard on the machine and actually carves a bit faster. Why? Without feathering of the pierced rectangle, the bit has to stop and plunge at the rectangle edge. With feathering, it instead starts at the surface and smoothly lowers as it travels in the y direction.

To eliminate the unnecessary carving, draw a rectangle at the left side of the board. Dimensions are not critical as long as you span the excess carved areas. Click on Carve Region and set the depth to .001. Right click on the right yellow dot and select Attach. Move the cursor over to the vertical centerline and click. Enter 2.45 (it should be 2.5, but there’s that darn Floor Feather again! If you want the cylinder to be exactly 5" long and not 4.9", do you know what to do?). Mirror the rectangle horizontally.

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I’m going to assume that you have a table saw, miter saw, band saw, or some other saw to cut off the ends of the cylinder after it has been machined on the Carvewright. If not, let me know, and I’ll show how to do this on the Carvewright.


Extra credit: In the Carvings list, select the top rectangle and the two wedges. Click on the Group button at the bottom of the Carvings list. Select the Group that you just created, then click on Make Pattern, and save the pattern in your choice of folder. Start a new project and select and place the pattern that you just made. What do you think?