Patio's projects

The Photo Album is a place for "Shop Shots" as well as pictures and descriptions of projects that we are working on. Show off your Shops, Machines, and your Projects!

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Harold_V
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Re: Patio's projects

Post by Harold_V » Wed Feb 21, 2018 2:42 am

Lookin' good!
Did you notice how much faster things went this time, in spite of doing more work?

H
Wise people talk because they have something to say. Fools talk because they have to say something.

Patio
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Re: Patio's projects

Post by Patio » Thu Feb 22, 2018 2:07 am

All the material I have used to date, was scrap when I got it. So now it is still scrap just in another form.

Harold, yes it get faster, but not always easier. :?

For the amount of work I put into engineering this thing, It has not gone very well.
Today I made the mounting plate. I got the hole locations wrong and had to widen the slots just a bit to make it work.
I also made the potentiometer pulley. It did not end up on the same plane as the idler pulleys and is the wrong size to function properly. I messed up the math somewhere.
It is all repairable. I will make the idler bushings a little taller to align them with the pot pulley, and the pot pulley needs to be smaller, so I can just turn it down and cut a new groove.
I will get it right sooner or later! :)
20180221_224951a.jpg
20180221_225018a.jpg
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Harold_V
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Re: Patio's projects

Post by Harold_V » Thu Feb 22, 2018 2:43 am

It takes a lot of practice to make things that work right out of the gate. So many things to keep track of, and it's all too easy to miss a detail or two. Nice thing is, it's all experience, so you should be improving, and I expect you are. That's pretty work. You'll get better about little things like missing a slot location.

I know of no one who was born with machining talent. Some folks are somewhat more inclined than others, but each of us must make our share of mistakes (I got more than my share) in order to become proficient.

If, in the process of reducing the pot pulley diameter you find you don't have enough traction to drive the pot reliably, you can always add an idler pulley, located at approximately 5:00. That should give you about 270° of wrap around the pot pulley.

You have the right mindset. Success will come with experience.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

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GlennW
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Re: Patio's projects

Post by GlennW » Thu Feb 22, 2018 8:01 am

So, was the model you made incorrect, or were the parts made incorrectly?

I make three view drawings of things before making them and it always seems to work out. A lot of times, depending on what I am making, I only draw a single view that only shows what is needed such as hole locations.

I decided to try modeling and and spent a few nights figuring it out, but just never found any practical use for it as far as actually making things. (I guess I'm just old, as I still don't have an Iphone either...)

For your part, I would have drawn a side view starting with two parallel lines. One being the face of the plate, and the other the center line of the belt, and worked from there.

For the plate I would have drawn a square of appropriate size and added the hole locations and the dimensions of the cutout.

Pretty much exactly what you show in your two images and about ten minutes of drawing in AutoCad once the dimensions were known.
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!

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NP317
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Re: Patio's projects

Post by NP317 » Thu Feb 22, 2018 11:02 am

Not having any CAD software available, I often just make pencil/pen sketches prior to machining parts.
Some days I might even use a strait edge. I've even been known to make actual orthographic projection drawings!

So I've made my share of dimensional mistakes during fabrication.
You've got my sympathy.
Call it Hit and Miss Engineering design...

Your eventual results always seem good.
~RN

John Hasler
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Re: Patio's projects

Post by John Hasler » Thu Feb 22, 2018 2:58 pm

All my mistakes are the fault of the guy who does the drawings. It's always the same guy, too...

Patio
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Re: Patio's projects

Post by Patio » Sun Feb 25, 2018 4:04 am

Hi everyone,
John, I know that guy! :)

RN, I could draw this project on paper pretty easily. I was fortunate enough to have gone to school when they still taught mechanical and architectural drawing. I am in the process of teaching my self to draw in Fusion 360, so I try to draw things up to get clearances and dimensions. I am also learning to do it in such a way the the parts and assemblies can be edited easily. Once the model is made, it can have it produce drawings, with any of the dimensions that one selects. Which is what I would like, so I can take them to the shop to make the parts. The program will also generate g-code for cnc machines to use. I have drawn a rack and pinion, rotating, and belt versions of the mechanism. I chose the belt mechanism as I believe it is the easiest to connect to the machine.

Glen, I changed a couple dimensions during the making of the parts and missed relating dimensions somewhere. So I have been penciling in the dimensions I need as I go.
Then I totally messed up the calculation of distance to rotation. :oops:

I have all that sorted out now and have built the new parts and assemble them.
20180224_234347a.jpg
20180224_234506a.jpg
The problem I am having now, has to do with the belt and it's traction on the small pot pulley. I even took Harold advise and put in an extra idler to increase the amount of wrap around the pot's pulley. The belt is Buna O-ring. I started with a smaller diameter O-ring, but the amount of stretch it had was a problem when changing directions, as the slack has to be taken out, in the opposing direction, before the pot gets movement again. I tried a thicker O-ring but still barely get enough traction on the pot pulley, and I don't think is will be reliable in use. I had originally thought about using a timing belt set up, but figure if it worked with O-rings, It would be easier to build. I am going to try a couple of things to see if I can get enough traction to make it work. Otherwise I will order some belts and pulleys.
Any thoughts on this?
Live for the moment!
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Harold_V
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Re: Patio's projects

Post by Harold_V » Sun Feb 25, 2018 5:24 am

One of the problems with traction may be related to the uneven pressure applied to the shaft of the pot. It may not like having side pressure. You may have to entertain the idea of multiple turns around the pulley and use something different to transmit motion if that's the case. Something on the order of an old analog tuner (variable capacitor, if memory serves) in AM radios. It also may respond favorably to reduced tension on the O ring. Hard to say, as I'm only assuming that's the problem.

Very nice looking work, Patio.

H
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warmstrong1955
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Re: Patio's projects

Post by warmstrong1955 » Sun Feb 25, 2018 7:41 am

I think you just need a deeper groove in the pulleys, to get some more friction, now that you have increased the thickness of the o-ring belt.
In the pics, the belt looks to be sitting pretty high in the grooves.

Just a thought.

Bill
Today's solutions are tomorrow's problems.

JackF
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Re: Patio's projects

Post by JackF » Sun Feb 25, 2018 10:47 am

Not that I have any expertise in this area :roll: but I think Bill has nailed it; the belt needs to ride lower in the groove. :) :) However, from the pics it looks like you may need wider pulleys to accommodate the bigger (wider) belt.


Jack.

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GlennW
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Re: Patio's projects

Post by GlennW » Sun Feb 25, 2018 1:41 pm

Perhaps two changes at once is biting you.

The original belt fit the pulleys but didn't have enough redial contact on the pot.

Then you added the idler and also went with a thicker cross section belt.

Perhaps trying the original cross section belt with the idler is the solution.
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!

Harold_V
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Re: Patio's projects

Post by Harold_V » Sun Feb 25, 2018 4:58 pm

In fact, depth of belt in the pulley may just be the answer. V belts grip the tapered portion of the sheave, wedging the belt so it drives properly. By increasing pulley diameter and widening the pulley, the groove could be cut to the depth required to achieve the correct movement of the pot, but a thou or so narrower than the O ring diameter, so it wedges in the groove. That should increase traction immeasurably. That, of course, would require that the belt (O ring) be stretched very little, otherwise the diameter of the O ring is reduced.

Using O rings for a drive is quite acceptable. The spindle of my 1 horse B&S surface grinder is so connected to the motor, although through a series of six O rings.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

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