[guru_florida]

Here are some pictures of my homemade bellows. This is the first ones I made that I consider a success. The bellows are made with 18mil black garden rubber matting on the outside, 20 mill rigid plastic sheet as the inside ribs, and 4mil red duct tape on the back. The duct tape on the back is not really necessary as the ribs are glued to the matting using superglue, but I think it adds a litter more strength and protection.

It's not really duct tape but drywall finishing tape. The plastic rib sheets were kitchen cutting sheets I bought at Winn Dixie on sale for 50 cents for 4. (You probably wont find any more, I couldn't, discontinued I believe.) Anyone find a source for this type of plastic sheets let me know.

The rib pattern was cut out of the sheets using my cnc machine and a pcb milling tool. I will post the cnc code after this message. The gcode is paramatized self coded.

Initially my gcode cut a pattern that made small bridges between the ribs so I could lay a whole sheet of ribs down at a time and afterwards the bridges would probably break off during normal use. However, glueing a whole pattern down at a time became very difficult and the cutting time was much longer. A simpler gcode cut that cut individual ribs, but a lot of them, worked better. I then layed them out perpendicularly on some duct tape with the proper separation. I then glued this strip on the matting, glueing each rib individually but using the tape to keep things aligned. Once all the ribs were placed the tape was peeled off carefully. Once all ribs were placed, I then carefully placed rows of duct tape over the back of the bellows as shown in the picture to protect the bottom.

This is preliminary instructions still. Let me know what you think. If there is interest I will take more pictures of the assembly for the next bellows.

pros:
seems durable, should be well resistant to oil and swarf
flexes easily from max expansion to max compression
cheap, under 20$

cons:
This bellows max compression is 3 inches. Thats 6 inches for each axis lost on my table of 16" travel. However, this can be compensated by extending my axis beyond the travel length. In detail, it is the corner folds that make 3 inches, the center of the bellows max compression is 1.5 inches. If a pattern can be made that doesnt have this style of fold the compression width could be halved. ideas?

[guru_florida]

Here is the rib pattern code:

(Protective Bellows rib generator)
(The following program generates rib sections for making fully paramitized protective bellows)
(originally coded for emc2 - linux cnc project)
(C2008 Colin MacKenzie)
(http://www.colinmackenzie.net)
(cnczone.com member guru_florida)
(the useful variables)
#90=-7.5 ( x origin start/finish )
#91=-6 ( y origin start/finish )
#92=40 ( cutting feed rate )
#101=7.5 ( Length of each center spar, inside measurement )
#102=2 ( Length of each side spar, inside measurement )
#103=0.52 ( Width of each spar )
#104=20 ( Number of spars to cut )
#105=45 ( angle of spar cuts )
#110=0.1 (travel or jog Z depth)
#111=-0.06 (begin cut depth)
(computed often-used variables - dont change)
( the Y value of the triangle formed by the crest and root is )
( known, it is #103, the x value is not, we calculate it here )
#501=[#103*TAN[#105]]
#511=[#101+2*#501] ( length of center spar long side )
#512=[#102+#501] ( length of side spar long side )
( Compute the opposite ends of our pattern )
#502=[#90+#511+2*#102] ( the x end )
#503=[#91+#104*#103] ( the y end )
( lets print out some interesting variables about the setup )
(print,Some valuable measurements you may want to know:)
(print, Zig Zag : Angle=#105, X=#501, Y=#103)
(print,Center spars:)
(print, Length long side : #511 )
(print, Length short side : #101 )
(print,Side spars:)
(print, Length long side : #512 )
(print, Length short side : #102 )
 
( main program start )
G90
T2 M6
G0 Z#110
G0 X#90 Y#91
( cut verticle lines )
#51=#91 ( will hold the y value iterator )
O1 while [ #51 lt #503 ]
G0 Y#51
G1 Z#111 F#92
G1 X[#502]
G0 Z#110
#51=[#51+#103]
G0 Y#51
( cut backward )
G1 Z#111
G1 X#90
G0 Z#110
#51=[#51+#103]
O1 endwhile
 
( cut zigzags through the lines separating the edges from the center )
#52=[#90+#102] ( our x position of zig zag start )
#53=#52
#51=[#51-#103]
#600=#51 ( save the current Y position )
G0 X#52 Y#51
O2 while [ #51 gt #91 ]
G1 Z#111 F#92
#51=[#51-#103]
#53=[#53+#501]
G1 X[#52+#501] Y#51
O3 if [ #51 gt #91 ]
#51=[#51-#103]
#53=[#53-#501]
G1 X[#52] Y#51
O3 endif
O2 endwhile
G0 Z#110
( cut zig zags up the other side )
#52=[#502-#102-#501] ( our x position of zig zag start )
#55=[#52-#53]
(print,Check: length of spar on bottom of pattern : #55)
G0 X#52 Y#51
G1 Z#111
O4 while [ #51 lt #503 ]
G1 Z#111 F#92
#51=[#51+#103]
G1 X[#52+#501] Y#51
#51=[#51+#103]
O5 if [ #51 lt #503 ]
G1 X[#52] Y#51
O5 endif
O4 endwhile
( cut the bounding box )
G0 Z#110
G0 X#502
G1 Z#111 F#92
G1 Y#91
G0 Z#110
G0 X#90
G1 Z#111
G1 Y#600
G0 Z#110
G0 X0Y0
M30
%

[samco]

Sweet. Nice work

sam

[hybidder]

Looks great!

I have been wondering about trying to make some covers for my bridgeport II type machine. I think you might have just given me an answer as to how to go about it.

Keep up the good work and keep us posted....

[Oldmanandhistoy]

If a pattern can be made that doesnt have this style of fold the compression width could be halved. ideas?

Can you increase the hight of the cover to reduce the number of folds needed?

I have been working on a similar idea and have been looking for a suitable cover to go over my stiff'ish plastic under layer. You mentioned "black garden rubber matting" so I will give the garden centre a go.

Thanks for posting,
John

[guru_florida]

Yes, you can increase the height of the ribs. See the parameters at the top of the gcode file (width of rib, currently 0.55). I thought of doing that after this last bellows, but I am not sure I have the room to go much higher. I have some math formulas I will include for calculating the expansion and compression results based on material thicknesses. I may also try a 5 or 6mil painters black matting instead of the 20mil garden matting.

In the picture, I have installed some aluminum channel at the bottom sides of my bottom axis and installed the bellows (but not actually secured.) Its a great fit!

To solve my my problem of losing 3 inches per bellow, I think I will redesign the end of my axis. I will have the bellows cover over the motor as well so the 3 inches will be gained back. During compression the bellows have a *slight* tendancy to want to buckle upward. I will have a metal cover over the top of the bellows but just over the portion that covers the motor. This pocket over the motor section will ensure the bellows dont buckle upward as they are compressed, rather the bellows will fit neatly into the pocket. To further illustrate, during full compression imagine not seeing the bellows at all as the axis carriage is butted up against the end of the pocket.

Math:
(so far, my constructed bellow concurs with these formulas )
W = Width of bellows
Wc = Width at max compression
Wr = Width of rib
n = number of ribs
s = separation
x = expansion coefficient (80% typical via emperical methods)
w = thickness of material sandwich while folded

W = (Wr+s) * n * x
n = W / ((Wr+s)*x)
Wr = W/n/x - s

Width at Max compression:
Width measures at corner edges, but half this at center. Corner edges are limiting factor.

Wc = w * n


In my case,
W = 17.9
Wr = 0.55in
n=32
s=0.150in
x=0.80
w=0.1in


By using 6 mil black painters tarp the max compression width would be slightly less than 2in. With rib of rib increased from .55 to .75 it would be further reduced max compression to width of 1.41in.

[guru_florida]

I have been working on a similar idea and have been looking for a suitable cover to go over my stiff'ish plastic under layer. You mentioned "black garden rubber matting" so I will give the garden centre a go.

What did you use for your stiff'ish plastic under layer? How did you cut it and with what tool?

Thanks,
COlin

[guru_florida]

Tried 6mil painters tarp, it didnt work so well. The glue doesnt stick to it at all. The red tape holds it together so it would work but I dont know how well it would stay after much usage.

C

[Oldmanandhistoy]

Yes, you can increase the height of the ribs. See the parameters at the top of the gcode file (width of rib, currently 0.55).

I was asking the question if you can increase the height to give you more compression.

What did you use for your stiff'ish plastic under layer? How did you cut it and with what tool?

My original idea was to make a plastic mould and use liquid Latex to form the bellows but it did not work out well. Getting a uniformed thickness was the main problem. I have been since trying to get round to finding thin rubber sheet to cover the plastic but as yet not found the time.

The plastic sheet came from an A4 paper folder I had lying around, not very thick so easily cut with a craft knife.

I have the template on my mill to see if the joints would crack under continuous bending/straightening. So far so good but I need to clear the chips often to prevent them piecing the plastic which a thin sheet of rubber will prevent.

John

[Oldmanandhistoy]

I’ve been quite busy today making a coolant and chip guard for my mill (amongst other things). I’ve used fish tank silicon to seal the corners of the polycarbonate enclosure and it occurred to me why not try a layer of the silicon on my plastic bellows. Well to cut a long story short I have applied a layer and will see how things turn out. I feel quite confident that this might be the answer to the home made bellows.

In the mean while if any one knows what you can use to thin out silicon sealant please let me know as its a bit thick straight out of the tube.

John

[guru_florida]

I was asking the question if you can increase the height to give you more compression.

Yes, What you are thinking of as height, I am thinking of as width. It depends on when you are considering the dimension, as it is a sheet of paper and laying down (width) or in a compression state (height). Am I correct?

So my height is 0.55 with .153 separation, so approx 0.70 in.

My original idea was to make a plastic mould and use liquid Latex to form the bellows but it did not work out well. Getting a uniformed thickness was the main problem. I have been since trying to get round to finding thin rubber sheet to cover the plastic but as yet not found the time.

I thought about this too! Glad to hear about your experience. I also thought of taking an mdf board, deeply embossed with my pattern, then rubber glueing razor knife type blades in the gulleys. Then using this as a kind of punch. I could cut my pattern in seconds. I may still try this.

The plastic sheet came from an A4 paper folder I had lying around, not very thick so easily cut with a craft knife.

I would like to enumerate all the available plastic sources if other people are to duplicate our designs.

C

[Oldmanandhistoy]

Yes, What you are thinking of as height, I am thinking of as width. It depends on when you are considering the dimension, as it is a sheet of paper and laying down (width) or in a compression state (height). Am I correct?

Height as in while in a compressed state; looking at your picture post #6 it looks to me the bellows could be higher. Fewer folds would require less space for them to compress into with the same coverage.

The silicon layer has now cured and although a little thin in one or two small areas seems to be the solution.

My bellows will cover 10” when fully extended and will compress into approximately 0.5” when compressed tight. I need to put it back on my mill and put it through its paces to see if the silicon will peel (not very lightly considering it is used on glass with a LOT of water pressure when used as intended). The other thing is how coolant and chips will affect it but I don’t foresee a problem there.

As for the plastic I have used it may be a bit to stiff so an alternative might be necessary.

Will post here when I have more info on how they are working out on the mill.

John

[guru_florida]

Can you explain how you laid the silicon onto your plastic? did you layer the top and bottom? How thick was the layer? Exactly what brand/product of silicon did you use?

Post a picture if/when you can, I would love to see it.

Thanks,
Colin

[Oldmanandhistoy]

Can you explain how you laid the silicon onto your plastic? did you layer the top and bottom? How thick was the layer? Exactly what brand/product of silicon did you use?

Post a picture if/when you can, I would love to see it.

Thanks,
Colin

Hi,

I applied the silicon with a plastic spatula type tool but would have been easier if the silicon was thinner, then I smoothed it with another wet spatula. I would estimate the thickness to be between 1mm and 2mm (0.039”- 0.078”).

Silicon was applied to the top surface only.

Brand is Juwel and came in an 80ml tube colour black. http://www.warehouse-aquatics.co.uk/...cone-518-p.asp

I took some pictures but they did not come out very well (flash) I will post a couple and you can let me know if they are any good. I will take some more and post them tomorrow if need be; unfortunately I reinstalled them on the mill before you asked.

John

[guru_florida]

Take a look at this link. I wondered how those telescoping protection bellows worked. Perhaps something simple and cheap can be worked out with metal sheet and Popsicle sticks?!?

GLADIATOR