Power Hack Saw help needed

[Jon]

In the US, even a still valid patent does not prohibit you from making one for your personal use, you just can't make them to sell.

We often see people saying that we are allowed to reproduce patented inventions for personal use; I would criticize you for repeating this, but I've made the same mistake myself! After researching it more thoroughly, here's what I think is happening:

First of all: US patent law forbids making or using patented inventions, even for personal use. These days, this is usually for a period of 20 years.



More: https://www.law.cornell.edu/uscode/text/35/271

Why do we get this wrong so frequently? My theory: it's caused by conflating patent law with the fair use doctrine of copyright law. Certain uses of copyrighted material are considered to be perfectly legal "fair use". There are four factors used to weigh fair use in copyright:

1. purpose and character of the use
2. nature of the copyrighted work
3. amount and substantiality
4. effect on the market

The "purpose and character" factor specifically includes whether the use is commercial or non-profit. And of course the "effect on the market" factor focuses on commerciality. So, if you have a non-profit use of a copyright that's not significantly impacting the market of the copyrighted work, you often have a strong claim to fair use.

Here's the rub: the concept of fair use applies to US copyright law, but NOT to US patent law. I'm not sure why this is, but I think that's the source of the frequent confusion.

Internet armchair lawyering aside: litigation over someone making a patented device for personal use is extremely rare, and usually not cost-effective. The worst I've ever seen, in almost two decades on forums, is a patent owner complaining to a forum admin about someone posting a how-to about making the patent owner's invention. It is almost never worthwhile to sue over this type of hobbyist use.

I believe there is also another nuance regarding making patented inventions solely for the purpose of research, but I would need to confirm this with an IP lawyer before understanding it fully. Let me know if anyone knows more about this.

I agree with all of your other points. The vast majority of patents are expired, searching patents is a great way to get ideas, and - in a healthy society - the government wants people to examine all of the public patent documents and drawings so that we can advance each others' inventions.

[olderdan]

There are a lot of these on HMT.
I would try and avoid the rocking frame type as it imparts a curved motion to the blade.
I built one like that and was disappointed with the result as I could not stop it blade bouncing, It did however help build a better one which I have been happy with, the frame runs on four bearings and is very smooth.
http://www.homemadetools.net/forum/h...6648#post84095
You are better of cutting tube etc with a chop saw as it will strip the teeth of a blade you use for solid stock.
Frank nailed it with two steps forward and one back but its the two forward that keeps us at it.

[Frank S]

At one time I was a part owner of a company which held several strong patents on one of their products. In my research development and prototyping section over a weekend I completely redesigned and built a new prototype scale model of the machine which would have circumvented all of their previous patents and save for one which was the most important patent of all of them. this also meant the new model could still be protected under the umbrella although while building the model I did notice a way to get around even that one Which meant the company needed to re submit the new changes to be added to their patents unfortunately for them they rushed the new model into production and their patent attorney drug his feet in getting the applications through in a timely manor. One of their distributors in Ca started producing the machines in Mexico, while still ordering his set minimum quota he started flooding the market with cheaply manufactured machines identical in looks only one these started failing and even got a few persons badly injured the company found itself up to their ears in litigation's Serial numbers and production records were the only thing that saved them.

[garage nut]

I agree wit the bouncing blade. I have watched "hours" of Youtube to try and make up my mind. A lot I think has to do with the speed. One guy is running it so fast the machine actually moves on his work surface.

Perhaps if I can get some more ideas how to limit the friction without compromising the accuracy in the slide idea I could be swayed to go that way.

[garage nut]

So I have spent some more time on YouTube and found that one person added a spring between the crank and the frame.

So as the crank goes down it puts tension on the frame. On the reverse stoke the crank raises and takes the pressure off the blade.

Also a half scale mock up using plans received from Nelson. Seem to work quite well.

[ncollar]

Garage nut
The only thing you need to make sure of is that your motor is turning in the right direction. As the arm is down it pulls and the cutting needs to be on that stroke. Looking good, now it is time to make the real thing.
Nelson

[garage nut]

Am going to use a wiper motor so 12V dc is easy to control direction.

Any thoughts of using a pneumatic cylinder as a power source?

[olderdan]

You need a fair bit of power to run a hacksaw machine, a 12v wiper motor is not going to provide that and any motor can be reversed.
I suppose a pneumatic cylinder is possible but that means you will have to run a compressor at the same time.
Are you limited by your workshop equipment or just over thinking the project?.
It will be interesting to see what design you decide on.

[ncollar]

Garage Nut
I have been looking at a couple near me and the one that I've seen uses the counter shaft as the pivot point. A bearing will be needed at that point and doing it this way you can make the saw as compact as you want in stroke. I'll be posting pics soon.
Nelson
The air cylinder would be nice as far as power but I do not think it would be worth all the work required. You would need to have a slide valve to get you forward and back. Good luck

[garage nut]

Couple of improvements.

Use Rod ends as bearings and orientate them in such a manner that they give me the ability to true up the blade once the machine is all built. We all know how quickly errors add up and then multiply it by a very long main frame member.

When drawing up the machine using the original 5.5" stroke to see what to change to get a 10" stroke I realised that the longer I make the rear pivot frame (old engine con rods in the design) the less the blade was rocking and the more it started to move like a conventional power saw. So my drawing now shows the rear pivot frame as pivoting at the base of the frame holding the whole machine together.

I am also questioning the wiper motor idea, but I have seen it on YouTube and it works. Not sure for how long..This machine will not be used for thin walled tubing. I think that type of profile will be a wiper motor killer, but as long as you have 50mm of steel in contact with the blade at any time and not tension the spring up too much I think it will last for the DIYer. If it fails it is an easy conversion to the more traditional multi pulleyed reduction design.

I always have a compressor full of air and was just wondering about the application. I have seen a few on YouTube, but they seem to move too fast and erratic to be accurate. Also only seen them cut PVC tube, so for now it will be an electric motor.