Need Help with Foam Cutting Machine

[lbbuild21]

I am working on a cutting machine for foam and am having a hard time finding the correct motor for the job. I have figured out that using an oscillating saw works best to cut through the foam. The foam is a closed cell 2lb density crosslink. I have a chute that holds the foam in place while the cutter slices a trapezoid shape groove on the top of the foam piece. The cutter works great when it is in the perfect position. However, over time, the position of the cutter moves making the cut not to specs. I need to make a cutter that is better stationary on the chute. My ideal one would be an oscillation motor fastened to an adjustable plane with the blade placed in the chute. I believe that I would need an eccentric or ultrasonic motor but cannot find one equivalent to an oscillating tool.

What motor or machine would work best to make a successful cut similar to a 20,000 OPM oscillating tool? Any assistance is much valued. Thank you for your time.

 

[btrueblood]

You will probably have more responses, and better ones, if you include a sketch of the problem, or a picture. Why exactly does the position shift, and can you not better retain that cutter mechanically to prevent movement/shift? An oscillating tool, like a handheld one? Is this for work or a hobby project?

 

[lbbuild21]

Here are pics of my current cutter set-up with the cutting blade, along with a sketch of it. I've also attached a sketch of how I would ideally like the set-up to work.

Yes, I am using a handheld oscillating tool as it makes the most effective cut. I currently retain the tool in position with steel hose clamps and vice grips so that it's easier to adjust the position of the blade to get the cut I need. Ideally I would want a motor bolted in the position that I need on the chute (similar to the Desired cutter sketch). I can't figure out how to make the oscillating tool not vibrate so heavily to where it moves the position of the blade out of the correct place. I have to make many adjustments to get the exact position I need and it doesn't take long for the blade to shift due to the vibrations and the way I have the tool secured. Even a minute shift in the position of the blade will make the cut not accurate.

This is where I'm at with the device but I'm not sure it's the best approach. I think if I can make a motor able to mount stationary to the frame of the chute in the needed position then that will allow the cuts to be accurate every time. I'm just not sure on what type of motor would be sufficient. The blade is approximately 7 inches in diameter so the motor needs to be powerful enough to move the blade efficiently, targeting at 20,000 OPM.

This is a work project that I have been stumped on for some time. I'm in the R&D phase and can't move forward without a successful prototype.

Set-up:

Blade:

Current Set-up Sketch:

Desired Set-up Sketch:

 

[TugboatEng]

The gear case on your oscillating tool has & bolts that attach it to the motors. Use these holes to mount the tool to a metal plate that you can use threaded rods and bolts to adjust and secure.

 

[MacGyverS2000]

However, over time, the position of the cutter moves making the cut not to specs.

Given this type of Mickey-Mouse setup, is it any surprise things move? How can you hold any spec with that?!

Dan - Owner

http://www.Hi-TecDesigns.com

 

[btrueblood]

A hot wire cannot be used with the foam?

20,000 oscillations per minute...are you sure that little tool actually produces that speed with such a massive blade (relative to the small blades it probably came with)? Have you measured it? And verified that this actually cuts the foam, not just make noise while you mechanically shear the foam with force alone?

As Tug said, you will want to find a method to bolt to the metal parts of the gearbox, if possible. Better, come up with a heavier and more robust gearbox/eccentric and drive motor.

 

[MintJulep]

Using this parts diagram for a similar Bosch tool you could begin to imagine where opportunities to design an improved mount might exist.

https://www.boschtoolsservice.com/O...=3601B31010&mn=GOP40-30B&RelatedTools=&init=1

 

[btrueblood]

Excellent advice, Mint. It also gives you a source for new bearings and cams, motors, and housings, once the old ones have destroyed themselves...

 

[lbbuild21]

First off, addressing smartass MacGyverS2000, I am aware that the setup is shifty. That is exactly why I am on an engineer forum, for professional opinions and expertise. This setup is my first process to figure out if the cut is possible and product is effective for the application. I am not an engineer. I would love to hear your thoughts and layout of an ideal operational cutting machine, minus any lighting effects. If its not worth your time, then please don't waste mine.

TugboatEng that is the exact vision that I initially had. I have attempted to deconstruct an oscillating tool to see if I can utilize housing to mount to a plate. However, I could never get the motor to operate after deconstructing it. Like I said, I am not an engineer and the mechanics of an oscillating tool, especially trying to reverse-engineer one, is a little too over my head.

I first started with hot wire to cut. The wire gums up quick due to the density of the foam and needs a great amount of heat to maintain cutting temperature. That is why I tried other methods and landed on an oscillating tool as the most effective. I agree the 20,000 OPM is not what the blade is moving at since it is so large. I have not measured it, but have verified that it does cut the foam. I am honing in on a heavier motor, but that is where I am stuck. I looked for similar motors, but haven't found one strong enough and able to be mounted like I want. The oscillating tool has a 90* angle from the motor to the crank housing shaft (driven by the drive bearing moving eccentrically between arms to the shaft).

Mint, I too think that is a great illustration that helps understand where to improvise. Thanks! I would like to use a stronger motor than a handheld tool, tho. Does anyone know of a heavier, mountable motor that can be tested?

I am located in San Antonio, TX. I have tried talking to several companies from foam fabricators to mechanical engineers around Texas and none have given me any real traction. Most don't care to manufacture a custom cutting machine from scratch and others just simply can't make an effective cut. If anyone is around my area and interested, I would love to work with you and pay accordingly.

 

[3DDave]

I still cannot picture what the result is. Take some time and make a detailed scaled drawing of what is to happen to the foam and what the cutting action is supposed to do.

If this is intended to remove a slope sided flat bottom depression I cannot see where the removed foam can possibly go.

The tool needs a horizontal constraint on the vertical part of the cutting tool nose - a plate with an interference fit is required to resist the cutting loads.

A larger motor will likely destroy the gearbox.

Anyway - better documentation about what constitutes an effective cut would help.

I'm guessing you meant cross-linked polyethylene foam. It would be far easier, and is the only method I've seen used for such shapes, to cut the segments separately and glue them together. You would take the foam block and split it to three pieces, cut the middle piece to thickness and the bevels with a straight cutting electric knife and then bond the pieces together.

Or, start with a main block the thickness and width of the finished part and split off the tapered pieces from another block and adhere the tapered pieces to the top of the main block. This would decrease the waste material.

Because the blade will be longer than the cut a guide can be applied to the free end to prevent unwanted deflection.

 

[mfgenggear]

a small video might have been more helpful see this setup, how it functions.
suggestions
make cradle from aluminum instead of square tubing.
make two halves to clamp more securely. bolt the the to parts. but for a new similar design.
the angle grinder has a 90 degree bevel gear drive from the motor. so think about a small standard gear box with 90 degree gearing.
with out knowing the actual forces to cut the foam, a best guess would at least a 3/4 HP electric motor.
look a these possibilities. belt and pulley, easiest , chain drive, or direct drive. there are standard components out there.
and most of the vendors have on line calculators to run the forces, and required sizing. hire a consultant to address
the proper sizing requirement.

 

[BrianPetersen]

Is waterjet cutting a possibility?

 

[IRstuff]

Hot wire seems to work well for certain foams

https://www.youtube.com/watch?v=LLB0cq-CEgU

https://www.youtube.com/watch?v=tCxpEz9SOeM

Conversely, CNC foam cutting can also be doing with a routing tool

https://www.youtube.com/watch?v=AyvC0Ap7KuA

https://www.youtube.com/watch?v=cKRb-X4cwSM

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[TugboatEng]

Hot wire may harden the edge of the foam which would be a negative characteristic for a cushion.

CNC is completely unnecessary for a single dimension cut.

Ibbuild, you don't need to disassemble, just remove the 4 screws. You need to cut a hole in a metal plate to fit nearly over the head of the tool and use 4 longer screws to attach it to the body of the tool. With that plate attached you have many more options to restrain/position the tool.

 

[3DDave]

Not sure how much to expect - It's a Hyper Tough tool that costs $20 at Walmart.

A short exploration shows the Rockwell RK5142K 4.0 Amp Sonicrafter F50 has good adaptability to fixturing it and will likely produce much more cutting effect. It does claim 5 degrees of motion, but I don't know if that makes a difference. Most oscillating tools are designed specifically to be comfortably hand-held, which means no simple mounting surfaces - lots of plastic and padding. They also like the artistic tapered and complex curved castings for the gearbox.

https://www.amazon.com/dp/B01HD4EOR0/?tag=best-oscillating-tool-20

I would still look at oscillating knives - such as used for carving ham - and gluing sections together. Probably worse adaptability to fixturing, but use of expoxy putty would be worthwhile for the knife handle to produce flat and adaptable surfaces.

 

[MintJulep]

Have you considered additive manufacturing?

That is, glueing 3 pieces together.

 

[saplanti]

It is too difficult to cut foam mechanically. Hot wire is the best option.
Foams are moulded to the shape required. Did not see any white product or electronic product package? They are shaped to suit the equipment by moulding.

 

[Compositepro]

Use a band saw with a scalloped knife blade (used for meat cutting, among other things. Your oscillating knife blade is mechanically unstable, sort of like balancing a marble on the cutting edge of a knife. Any side force between the blade and foam causes deflection, which causes in even more deflection of the blade and foam. And both the foam and your blade will deflect very easily, resulting in an uneven cut. A knife does not create a kerf like most saw blades, so the foam stays in contact with the sides of the blade after the cut. The band saw also has this issue but is a lot stiffer.

Hot wire may also work well but be aware that it cuts by melting the foam with radiant heat from the wire, which causes the foam to reticulate away from the wire, and there is no physical contact with the wire. If there is contact due to trying to cut too fast or not having the wire hot enough, the foam will stick to the blade and burn, causing char to build-up on the wire.