# Pneumatic cylinder selection - Help caclulating the Force needed

• Misc.

## Summary:

I need to build a pill crusher with very hard sell. I dont know how to calculate the Newton Needed so that i will be able to select the correct Pneumatic cylinder
This is my first post in this great community.

English is not my native language, so i am sorry for any mistakes.
I need to build a pill crusher using a pneumatic cylinder with 30mm stroke (effective travel).
i have e metal container with 25mm base diameter where i have to make powder from 6-8 pills.
this pills have very hard shell.
I have an other metal cup that fits as male plug on this container so manually i press this on container to crush the pills.
Even if i add all my wight on it, about 90kg, the pills do not crush so i have to twist the cup at the same time.
i need to make a press , but because this machine should be portable i have to select the smaller , more lightweight pneumatic cylinder.
I do have a manual press, so i will upload the geometrical shape and dimensions, of the press and what force did i apply to the press to achieve the effect.
More specific i will stand on a scale and will find out how much Newton were needed to achieve the result ("Total bodyweight - wight indicated on scale" and then convert kg to Newton).

Welcome, Vatech
I would look at what is commercially available first.
It seems that rotating the pills between two dented surfaces is the normal way.
Just by steady compressing force seems to be difficult, not only because those things can be very resistant to compression, but because once crushed, the material remains under the plunge.
Even the old fashion mortar requires some rotation of the hand for that reason.

If the above is correct, you will need to engineer some mechanism.
Using a nut and screw type of press with pneumatic action may solve your problem.
Experimenting with several ways to crush those pills would give you an idea of the requirements of such mechanism and the required force or torque.

Welcome, Vatech
I would look at what is commercially available first.
It seems that rotating the pills between two dented surfaces is the normal way.
Just by steady compressing force seems to be difficult, not only because those things can be very resistant to compression, but because once crushed, the material remains under the plunge.
Even the old fashion mortar requires some rotation of the hand for that reason.

If the above is correct, you will need to engineer some mechanism.
Using a nut and screw type of press with pneumatic action may solve your problem.
Experimenting with several ways to crush those pills would give you an idea of the requirements of such mechanism and the required force or torque.
I tried using the attached press with all my weight on the edge of the handle with not good result.
My fist thought was to use a pneumatic cylinder with 100mm bore and a 6bar pump. By this way i would get 480kg of force.
The most effective way that i took good results was by manually hitting an other metallic container on a metal surface. By using impact, 2 hits were enough to create the powder. The top of the container is 200gr , so an expert could calculate by combining the acceleration what was the final force during the impact.
Dented surfaces keep a lot of powder, they have to be combined with nylon bags. This also increases the time needed for the process. I need a faster way. If i use the descriped cylinder and manually move the container to apply a second press?

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So, impact of two flat surfaces does the work?
If so, how do you plan to place the six pills on the anvil and to remove the crushed pills before and after each impact?

Was that mass of 200 grams free-falling? From how high?

Impact mechanisms work on the principle of building up potential energy and suddenly releasing that energy.
A heavy spring may help achieve the impact effect.
The pneumatic cylinder, hoses and mechanism could work on the potential energy.

So, impact of two flat surfaces does the work?
If so, how do you plan to place the six pills on the anvil and to remove the crushed pills before and after each impact?

Was that mass of 200 grams free-falling? From how high?
I have to do it portable and silent. So impace is not for me. I just mentioned it so that to let you know that high force is doing the job. There is a female metal container and a metal male cup from solid metal. So we place the pills on the "female type" container, place the male cup on top and then the impact comes not from free fall, we hit this from a distance of 40-50cm with high acceleration with the hand on a solid surface. so we get the powder. Usually most pills could be crushed by aplying the above container without impact, just vertical forc e and a litthe twist with the hand. But there are 3-4 pills that is absolutely difficult to crush them.
Here i fould a system that works with the impact method, but is very heavy and loud:

What i thing is to use a compact pneumatic cylinder for steady force, not impact and combine it with a rotation base of 15-30 RPM. I am an advanced user of Fusio360, but i have to find a way to design a moving base using thrust ball bearing, if i could find a ready solution that would be even better
https://www.aliexpress.com/item/323...ab45d7203dd2e6745-1596691139249-09264-_ePNSNV

I searched for rotary actuator to make the rotating base but i found for small diameter rotating bases only pneumatic systems which can not handle enough force. Any idea?

I see now; thank you.

• Why using pneumatics if you need your machine to be portable, silent and light?
Will you have available dried and filtered compressed air at all locations where the machine is going to be used?
If so, could you have the needed amount of pressure at each place, or a way to regulate it, since crushing force directly depends on that pressure?

• What are your capabilities for fabrication and available materials?
Could you machine the plunge, a cam, bearing housings, bushings, etc.?
Could you get big springs or relatively big pieces of rubber?

1) i would use a mini electric pump , 600kpa . The compact cylinder with adjusted speed is silent enough
2) Yes i can buy CNC service for aluminum and other harder materials.
My thought was to use and SDA cylinder for pressing the pills and design a small rotating base mountet on thrust bearing and by using a 35w 12rpm 55kg/fcm to rotate it. so i would combine those 2 movements needed.

An other idea is to create a Grinder - Mill , electric drived. but this can not be fast (i think) because whil rotating some pills will jump in the container
I am open in any ideas, because the idea i have now is not ideal.
i also thought of using the mechanism of en impact screwdriver because it combines the hummer effect and the rotation, but its very noisy

The maximum duration for crushing the pills should be less than 4sec

Lnewqban
...
The maximum duration for crushing the pills should be less than 4sec
...
Thank you.
This is critical to your solution.
How will you manage the pills moving in and out of your machine in such little time?
Even filling and emptying the pneumatic cylinder can consume much of that time.
Much depends on that detail.

Last edited:
Vatech
and i dont have axperience on pneumatic systems, that makes it even more difficult

Lnewqban
Thank you.
This is critical to your solution.
How will you manage the pills moving in and out of your machine in such little time.
Even filling and emptying the pneumatic cylinder can consume much of that time.
Much depends on that detail.

You are welcome, although I did nothing yet but asking questions.

I would analyze the whole process and time limitations before proceeding with the solution for crushing alone, which may result being the easiest of all problems to solve.

jrmichler
Mentor
Some more questions:

How many pills do you need to crush? One or two every day or so? Ten thousand per hour, 24 hours per day, 6 or 7 days per week? Some number in between?

Does your machine need to last for a few days, tens of years, or in between?

Do you need to crush each pill separately, keeping the powder from each pill separated? Or can you crush many pills at a time and put the powder in a bulk container? How large a container?

Have you tried crushing with a pair of pliers? A vise? Does simple compression (pliers or vise) crush properly, or do you need a sliding / grinding action?

Lnewqban
//How many pills do you need to crush? One or two every day or so? Ten thousand per hour, 24 hours per day, 6 or 7 days per week? Some number in between?
maximum 10 pills at once per medication. Lets say that it has to crush 250 medication in the morning and 250 in the evening 7days per week.

Does your machine need to last for a few days, tens of years, or in between?
//it should last one year untill some parts should be replaced.

Do you need to crush each pill separately, keeping the powder from each pill separated? Or can you crush many pills at a time and put the powder in a bulk container? How large a container?
//many pills can crushed at once and mixed, no problem. Powder will be given directly to patient via cups, so its better to use the same metal part as needed to collect the powder and not consumables

//Have you tried crushing with a pair of pliers? A vise? Does simple compression (pliers or vise) crush properly, or do you need a sliding / grinding action?
I tryed even on a bench to press the metal container and what was done was to compresed to one uniform powder- a new tablet was created. To work it need a little rotation-move during the press. Grinding takes time. even if i use high speed motor pills jump inside the mill, so 4 seconds can not be achieved (just a guess, i may am wrong). if there was a rotation of a modified "pyramid" surface combined with press then the result should be perfect
https://pillthing.com/products/heavy-duty-pill-crusher-with-container-item-71091

jrmichler
Mentor
Have you tried the pill crusher in your link? If so, how hard do you need to push? How many turns, or fractions of a turn, are needed? If you push harder, can you crush a pill or pills with fewer turns? Does it do an acceptable job of crushing? What is the time per pill, or batch of pills? How many pills can you crush before your arm wears out?

You need this information before designing your own pill crusher. And we need it to help you.

Have you tried the pill crusher in your link? If so, how hard do you need to push? How many turns, or fractions of a turn, are needed? If you push harder, can you crush a pill or pills with fewer turns? Does it do an acceptable job of crushing? What is the time per pill, or batch of pills? How many pills can you crush before your arm wears out?

You need this information before designing your own pill crusher. And we need it to help you.
Yes i have tried. Its good but needs too much force . with muscle force it just takes too much time
// If so, how hard do you need to push?
Some kind of pills require all the body weight to be pressed (900Newton)combined with rotation and even though it takes time
//How many turns, or fractions of a turn, are needed?
just a few degree its enough, not full rotation
// If you push harder, can you crush a pill or pills with fewer turns?
it has to be combined , if you press too much without rotating you will create a new tablet
//Does it do an acceptable job of crushing?
Absolutely not
//What is the time per pill, or batch of pills?
It depends on type opf pill. even one long time released pill, because of its hard structure takes time and efford //How many pills can you crush before your arm wears out?
The problem is that this should be used by nurses , not by me. so they will not have enough force even for one medication
You need this information before designing your own pill crusher. And we need it to help you.

Lnewqban
jrmichler
Mentor
So you need a combination of compression and sliding or twisting, and the compression distance is greater than the twisting distance. Here's an idea:

Use a large hex head bolt, say an M27X3 - 60 or 70 mm long. A conical depression with 118 degree included angle is easy to make because that is the angle of a twist drill. That size bolt has a head 41 mm across the flats, so it might be large enough that a normal person could turn it by hand. If not, weld a bar across the bolt head.

This is a solution and works. i have made custom cnc machined crusher with threads between the top and the container. But this takes time when there are many bedication to be given i very short time. thats why i want to do an autoamtic solution. I think i am in the wrong way, will try an other way and will come back to write if i managed to get the result

jrmichler
Mentor
So a solution with a screw thread works because it has a combination of compressive force with sliding. A good next step is to optimize the hand operated screw system. A fine thread, say 1 mm pitch, would provide a lot of force but require several turns, so would be time consuming. An extremely coarse thread, say a ball screw with 25 mm pitch, would operate quickly, but might not generate enough force or sliding.

Somewhere in between is a thread pitch that has just enough force, and operates with the minimum number of turns. Also, smaller diameter threads have less friction, so generate more force with the same effort. Acme threads have less friction than V-threads, and ball screws have almost no friction at all.

An optimized hand operated solution may well meet your needs. It does not need compressed air or electricity, nor does it have the safety hazards of a powered press.

A simple air cylinder is not a solution because it does not have the twisting / sliding motion. An optimized screw system would be a good starting point for a powered system. My recommendation is to first optimize a hand operated screw system, then add a power operator only if necessary.

Lnewqban
...
The most effective way that i took good results was by manually hitting an other metallic container on a metal surface. By using impact, 2 hits were enough to create the powder. The top of the container is 200gr , so an expert could calculate by combining the acceleration what was the final force during the impact.
...
I have made some less than rigorous assumptions and have calculated the force of that impact.
Because it depends on magnitudes that are difficult to estimate correctly, the calculated value of that force is not to be trusted, but can give us an idea about the effective crushing force that you would need.

The press in your attached pictures seems to be able to deliver a force of 2650 Newtons on the male plug when you use your full weight (90 kg-force) at the end of the lever.
That is equivalent to a pressure of 5395 kPa or 53 atm between 25 mm diameter male plug and metal cup.
If you have 8 pills of 6 mm diameter each inside the cup, the male plug could exert a pressure of 11705 kPa or 115 atm on all of them.

Your 100 mm diameter pneumatic cylinder-12/24 volt air pump combination seems to work, at least in theory.
The manufacturer of the pump claims it is able to supply 40 liter/minute (0.66 liter/second) at no-load condition, which could extend the shaft of your cylinder the needed 30 mm stroke (0.24 liter volume) in 0.36 second.

Vatech
So a solution with a screw thread works because it has a combination of compressive force with sliding. A good next step is to optimize the hand operated screw system. A fine thread, say 1 mm pitch, would provide a lot of force but require several turns, so would be time consuming. An extremely coarse thread, say a ball screw with 25 mm pitch, would operate quickly, but might not generate enough force or sliding.

Somewhere in between is a thread pitch that has just enough force, and operates with the minimum number of turns. Also, smaller diameter threads have less friction, so generate more force with the same effort. Acme threads have less friction than V-threads, and ball screws have almost no friction at all.

An optimized hand operated solution may well meet your needs. It does not need compressed air or electricity, nor does it have the safety hazards of a powered press.

A simple air cylinder is not a solution because it does not have the twisting / sliding motion. An optimized screw system would be a good starting point for a powered system. My recommendation is to first optimize a hand operated screw system, then add a power operator only if necessary.
In one of my first posts i wrote that this process has to be repeated 250times in a small period of time. so manually its not a solution for this case. The method would work

jrmichler
Mentor
Air compressors are rated in SCFM, or Standard Cubic Feet per Minute in English units. That's the air flow rate entering the compressor. The air flow rate out is in ACFM, for Actual Cubic Feet per Minute. So a compressor rated 0.66 liter/second will deliver 0.10 liter per second at 6.6 atmospheres pressure. That 0.10 liter / second is what moves the air cylinder.

Some thoughts:

There are hand operated presses with toggle linkages that might do the job. Simple, fast, and the toggle linkage provides the necessary force with easy hand operation. Here's a hand held one: https://www.midwayusa.com/product/1013017453?pid=665540 And a bench mounted version: https://www.midwayusa.com/product/1013020665?pid=807734

Is the twisting action necessary? The above posts seem to have it both ways.

By using impact, 2 hits were enough to create the powder.
I have to do it portable and silent. So impact is not for me.
Impact can be nearly silent. Impact is noisy when you have a light weight anvil setting on a table. Make the anvil heavier and set it on a rubber mat. If you experiment with the mass of the drop weight and the drop height, you should be able to crush in one hit. And the drop weight needs to be accurately guided so that it hits straight and on center, or it will rattle and bang.

Vatech and Lnewqban
You have correctly calculated that your pneumatic cylinder, once extended the 30 mm stroke with no resistance and increasing internal pressure up to the claimed 6 bars, could be directly pushing the male plug over the pills with a force of 480 kg-force or 4710 N.
That force will be 1.8 times greater than the 2650 N that you could develop with the full weight of your body via that lever of mechanical advantage (MA) ≈ 3 (according to measurements of the picture of your hand press).
Nevertheless, we don’t know if that force will be enough for crushing up to 10 hard shell pills.

You could replicate that force in your hand press by extending the handle with a piece of pipe and applying the weight of your body at a point located from the fulcrum at 5.3 times the distance between fulcrum and link of the shaft of the male plug (previously anchoring the press to the table).

The only crushing-effective test you have done with that 200 grams weight could help us roughly estimate the needed force.
You manually hit the metallic container on a metal surface twice to create the powder.
Calculating the final force during the impact is very imprecise, due to gross assumptions we have to make about acceleration and speed.
Here are my attempts:
For a free fall of 200 grams from the used height of 40 to 50 cm:

##V_f=\sqrt{2gh}~=~\sqrt{(2)(9.81)(0.45)}~=~2.97 m/s##
##E_k=\frac 1 2 mV^2=(\frac 1 2)(0.2)(2.97)^2=0.88~ Joule##
##F_{avg}~d=E_k##
Assuming a crushing distance (d) of the pills of around 1 mm:
##F_{avg}=E_k/d=0.88/0.001=882~N##

Now, using the extra acceleration provided by your muscles, I loosely assume that you could achieve between double and triple the velocity of impact respect to free fall:

For 6 m/s:
##E_k=\frac 1 2 mV^2=(\frac 1 2)(0.2)(6)^2=3.6~ Joule##
##F_{avg}=E_k/d=3.6/0.001=3600~N##

For 9 m/s (measured maximum speed of boxing punch):
##E_k=\frac 1 2 mV^2=(\frac 1 2)(0.2)(9)^2=8.1~ Joule##
##F_{avg}=E_k/d=8.1/0.001=8100~N##

Since there was no combined rotation in your test, perhaps less axial force than estimated will be needed for the worse case of 10 hard shell pills.

Practical considerations:

1) Rotation will be less effective on pills that fall in place close to the axis of rotation, as tangencial velocity will be minimum around there.
Perhaps devising something to guide the pills to avoid that location could drastically reduce needed crushing force and time.

2) The thickness or height of your pills will vary.
Consider quick adjustable location of the beginning of axial force application (which the pneumatic cylinder, as well as the manual lever, automatically do).
For a solution of fixed or lockable stroke, I would recommend a flexible element under the metal cup, like a strong axial spring or chunk of hard rubber.

3) Consider that, in the hand press of your picture, when inducing rotation with one hand, the force on the lever may be unconsciously reduced.
In order to avoid creating a new pill by excess of compression, I like the idea of locking the mechanism that produces the axial force, once a maximum value is reached; then, using rotation (under constant axial pressure) for breaking the pill by shear effect.

4) The press of your picture is wasting too much trajectory of the end of the lever.
The crushing axial distance may be in the range of 1 mm; that little thickness or height of the pill is what really needs huge crushing force.
Consider a quick-release mechanism that allows the operator to effortlessly locate the male plug directly in contact with the surface of the pills prior the axial force is applied.
That way, you could achieve greater mechanical advantage with a manual press, using the same amount of trajectory of the hand on the lever.

5) Finally, I don’t really like the idea of the air pump.
In my experience, those things are very noisy and very slow to increase pressure to the claimed values.
The one in your link works with 12/24 volts DC, which will attach you to a battery or converter or transformer.
If reaching the cylinder directly, the pumped air will accumulate humidity and dust inside the cylinder, which may reach a point at which the performance or reliability of the cylinder will suffer.

http://507movements.com/mm_140.html

http://507movements.com/mm_164.html

Last edited:
Vatech
I will thank you again for your help and i am happy to see that you love what you are dou
Air compressors are rated in SCFM, or Standard Cubic Feet per Minute in English units. That's the air flow rate entering the compressor. The air flow rate out is in ACFM, for Actual Cubic Feet per Minute. So a compressor rated 0.66 liter/second will deliver 0.10 liter per second at 6.6 atmospheres pressure. That 0.10 liter / second is what moves the air cylinder.

Some thoughts:

There are hand operated presses with toggle linkages that might do the job. Simple, fast, and the toggle linkage provides the necessary force with easy hand operation. Here's a hand held one: https://www.midwayusa.com/product/1013017453?pid=665540 And a bench mounted version: https://www.midwayusa.com/product/1013020665?pid=807734

Is the twisting action necessary? The above posts seem to have it both ways.

Impact can be nearly silent. Impact is noisy when you have a light weight anvil setting on a table. Make the anvil heavier and set it on a rubber mat. If you experiment with the mass of the drop weight and the drop height, you should be able to crush in one hit. And the drop weight needs to be accurately guided so that it hits straight and on center, or it will rattle and bang.
This can be a Solution for sure, althoug there is no rotation in this case and we might get a creation of a new tablet.
Althought i would like to make it fully automatic, meaning add a motorized mechanical movement or rotation