Calculate needed dimensions of table - Center of mass, levers etc

In summary: Wait, is this in the same room where you had to soundproof your practice drum set to keep from bothering the neighbors...? :wink:Actually, pretty close :D I'm not going to drill steel, though ;)
  • #1
interestedperson
9
4
My high school physics days are long ago ;) This is not homework, well, other than it is work, at home.
For a real application: Very space constrained "workshop", got a bench drill press, and want to build a table on wheels for it, to be able to move it into a corner when not needed.
Those wheels can each carry 100kg, got 4 of them, the drill press weights 54kg, so that should work for the wheels.

Now most of the weight is the motor unit, the cast iron foot of the thing will be bolted onto the table.
If I now apply a sideways force, like leaning against the motor case (or without extra weights, maybe sneezing at it!), the thing would fall over, if I chose table dimensions which are not much larger in the top surface area than the machine foot itself, says my gut feeling.

What I'd like to do is basically, compute what table dimensions I can get away with. The height does not have to be normal table height, working when sitting might be acceptable, it's only for occasional hobby stuff.
As drawn in the sketch below, I might add weights to the bottom of the table, to lower the overall center of mass.
(actually in the form of sandbags I have laying around, 25kg each, 2 might fit easily and leave the upper half for adding a tool drawer (optional))

I know the weights of the single parts of the machine. So I guess I calculate the center of mass of it all, including some assumed extra weight, make a simplified model where the left lower edge of the bottom of the table is a rotation axis, from it, a lever going to the center of the table bottom, from that, another lever going up to the center of mass. I also model in a sideways force with 1/2 my body weight or so, pressing at the motor case from the right, to the left, as if to make the whole thing fall over to the left side, around the axis that is the lower left edge of the table bottom.

Something like that?
Is there perhaps some free software to simulate that? There one could maybe see how quickly it would fall over if some excess force is applied sideways for a short period of time vs. whether it might just tilt by 2 degrees and recover... i.e. kinda like building it and trying intuitively whether it is sturdy enough, without having to waste material.

Untitled.png
The apparent little holes are an artifact, the material is supposed to be solid wood.
 
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  • #2
You could find the center of mass of the drill press and locate each of the caster wheels as far from it as practical, keeping around same distance between CM and each wheel.
Another idea is to make a lifting table, which allows you to lower the drill press prior to move the table around.

IMG_1633-Medium-e1509039958961.jpg
 
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  • #3
interestedperson said:
For a real application: Very space constrained "workshop", got a bench drill press, and want to build a table on wheels for it, to be able to move it into a corner when not needed.
Wait, is this in the same room where you had to soundproof your practice drum set to keep from bothering the neighbors...? :wink:
 
  • #4
berkeman said:
Wait, is this in the same room where you had to soundproof your practice drum set to keep from bothering the neighbors...? :wink:
Actually, pretty close :D I'm not going to drill steel, though ;) I have been drilling woods, plastic, softer metal for years with the battery hand drill, every now and then, no complaints, and other neighbors sometimes also build something.
I was very unhappy with the results of hand-drilling, so here comes the upgrade. Seeing you with the HAM gear there... I recently built a few indoor antennas to listen to local repeaters on UHV/VHF. The rods for the 70cm Quagi are not at nearly perfect 90° angles due to hand-drilling, grrr!

The lifting table looks cool. A bit involved, and I'd to get it right for this kind of weight & preferably not build a death trap.
 
  • #5
You have the right idea - make the base as low as practical, the base as wide and deep as practical, and add weight to the base. This base might give you some ideas:
Drill press.jpg

Add tool storage to the base. Start with drill press stuff, then add other tools until the space is filled.
 
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  • #6
For starters it seems to me that putting a drill press on wheels is a very bad idea. I would hate it I think.

My cheap tabletop drill press just sits on top of a heavy square table with no hold-down bolts and has always been stable enough. My design process followed from assuming the base supplied for the drill press was big enough to not topple and was centered.

I roughly found how far off the table top was the Center Of Mass and projected a rectangular pyramid from the COM to each corner of the base and on down. I made sure all the supporting table corners were slightly outside (bigger than) this imaginary pyramid (the base stack actually is an old 16 inch kitchen upper cabinet on 16"x16"x(8" tall) concrete block at floor).

The cabinet holds drill tools. Perfectly sufficient to my needs, cost next to nothing and took about a half hour to construct. I like having a small flat top at the drill base

A drill press is a very useful tool to have.
 
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  • #7
"it seems to me that putting a drill press on wheels is a very bad idea"

- those wheels have lockable brakes! I wouldn't do it without them. I hope they'll do their job well enough.
 
  • #8
interestedperson said:
the drill press weights 54kg
interestedperson said:
I have been drilling woods, plastic, softer metal for years with the battery hand drill, every now and then, no complaints, and other neighbors sometimes also build something.
I was very unhappy with the results of hand-drilling

That's a pretty heavy/big drill press for small jobs, IMO. So a few thoughts...

My first drill press was a small tabletop adapter to hold my hand drill vertically (with some angle adjustments), not a dedicated full-size drill press. Could that work for you for a while until you move into your own house with a dedicated garage/workshop?

I think that my next drillpress (when I had a garage/workshop) was more like 40 pounds, so a lot smaller than the one you mention. Why do you need such a large/heavy drill press now?

Assuming that you do really need the heavier drill press now, consider just laying it down on the portable tabletop to move it. Use C-clamps or similar to secure it to the tabletop for use, then lay it down to wheel it off to the side for storage.

When you have it vertical and are going to use it, consider clamping the portable table to something non-moving (like a wall or permanent table). Having a power tool running on a roll-around table doesn't seem like a good arrangement for safe operation to me.
 
  • #9
This kind of thing can work well, my neighbor has his bandsaw, drill press, etc on these. You tread down to lift just enough where the wheels contact the floor, to roll it around. When using the machine the wheels are "up."

roller_base.JPG
 
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  • #10
But do the wheels still gimble? I like the @gmax137 idea much better.
Hoping it will work is a bad way to start in my opinion...its your project!
 
  • #11
berkeman said:
That's a pretty heavy/big drill press for small jobs, IMO. So a few thoughts...

Perhaps. I had the Bosch PDB40 in sights first, available here everywhere... half the price of what I got now, and electronic speed control, 12.5kg weight. But it has some aspects I don't like usage wise, like the stupid wheel on the side. Some people complain about accuracy being a bit of luck (QC spread). From what I saw they don't give a number for guaranteed runout.

I looked at other more affordable machines, they had no electronic speed control as this one now also does not, but the one I picked had the widest (and also absolutely lowest) RPM range selacteble, if by manually changing the belt. I was looking at a materials vs. drill diameter vs. recommended RPM table, and the somewhat lighter machines looked all pretty useless in that light. Especially if I care about wood and plastic (and aluminum, brass). Since I wanted the search to end at some point, I took this one, despite the weight.

berkeman said:
tabletop adapter to hold my hand drill vertically (with some angle adjustments), not a dedicated full-size drill press. Could that work for you for a while until you move into your own house with a dedicated garage/workshop?

You mean like, in 2080? Not sure I'll make it.
EU is already working hard at making houses unownable for 'commoners'. And right now, you already have to be a millionaire to get one (that's not a dump / $$$ grave and 2h commute).

berkeman said:
I think that my next drillpress (when I had a garage/workshop) was more like 40 pounds, so a lot smaller than the one you mention. Why do you need such a large/heavy drill press now?
It's not necessarily the weight I need. The thing I selected for e.g. RPM happened to have this weight. One with "only" 36kg started at 600 RPM instead of 200, like all the others of simillar specs.

Then again, in forums with a lot of mechanical people around, you hear a lot "buy a used XYZ good old machine, not this new crap", and those machines sometimes weigh even double as much as this one ;) And cost a lot of money still.

Now seeing that arrangement with that forced-down wheel (by gmax137)... don't particularly like that exact arrangement, goes sideways way too much, it'll be in the way.

But seeing that, I guess I could turn it around, and install something that screws "stamps" towards the floor, to very slightly lift, or perhaps not really lift, but direct some of the force of the weight of the whole thing from the wheels onto those "stamps", which then act as additional brakes.
 
  • #12
interestedperson said:
don't particularly like that exact arrangement, goes sideways way too much, it'll be in the way.
That was just the first picture I could grab off Amazon, there are different designs out there. Most of them, you buy the rails and corner pieces, and use your own plywood. There is quite a bit of adjustability in size.
 

Related to Calculate needed dimensions of table - Center of mass, levers etc

1. How do I calculate the center of mass for a table?

The center of mass for a table can be calculated by finding the average position of all the mass in the table. This can be done by dividing the total mass of the table by the total length of the table. The resulting value will give you the distance from one end of the table to the center of mass.

2. What is the formula for calculating the moment of inertia for a table?

The formula for calculating the moment of inertia for a table is I = (1/12) * m * L^2, where I is the moment of inertia, m is the mass of the table, and L is the length of the table. This formula assumes that the table has a uniform distribution of mass along its length.

3. How can I determine the stability of a table?

The stability of a table can be determined by calculating the center of mass and the base area of the table. If the center of mass falls within the base area, the table is stable. If the center of mass falls outside the base area, the table is unstable and may tip over.

4. What is the principle of levers and how does it apply to a table?

The principle of levers states that a small force applied at a long distance from a pivot point can produce a larger force at a shorter distance from the pivot point. This applies to a table when considering the placement of heavy objects on the table. Placing heavy objects closer to the center of mass will require less force to balance, while placing them further away will require more force.

5. How can I use the dimensions of a table to determine its weight capacity?

The weight capacity of a table can be determined by calculating the maximum load that the table can support without breaking or tipping over. This can be done by considering the materials and design of the table, as well as the distribution of weight and the stability of the table. It is important to also consider the intended use of the table and not exceed its weight capacity to ensure safety and prevent damage.

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