Thread: Power Hacksaws V's Bandsaws

Originally Posted by shedhappens

Why exactly can't a worm gear be cut on a mill with a fly cutter ?

They can, but it depends on how good you want the gear to be. Ideally you want close and full contact between the worm and worm gear so that power transmission is smooth and continuous. To do that the worm gear is generally 'wrapped' around the worm a little rather than flat like a normal spur or helical gear.
You could use a fly cutter to cut the teeth - we will be using a formed cutter for the first stage but really that is equivalent to a fly cutter with multiple cutting edges. The hob is to finish off for a couple of reasons -

• Unless the fly cutter has a really small radius of swing, it won't be radiusing the bottom of the groove between the teeth. That will mean that the contact point of the worm may not be on the PCD, so transmission of power could be less than smooth. That may not matter with something that is only working in one direction or does not need exact speed stability.
• The form on a fly cutter also needs to be good to get the right shape. If we make a hob on a lathe there is probably a better chance of getting an accurate tooth form on the worm wheel as hobbing is a generative process.
• A worm is a helix. Over a small arc of contact the path of a helix will approximate a circle but as the contact arc increases there will be rubbing on the corners of the worm gear. Again, this may not matter if the rubbing is slight and the application is not critical

The replacement gear for Simon's saw has to fit into a pre-established space. As it was built with a commercially cut worm gear it should ideally be replaced with one. If a different gear type were used other changes could be required to make things work (and I'm not knowledgeable enough at the moment to know what they are). From links others have posted it looks to be (when working) a piece of kit worth taking the trouble to get back to as good a condition as possible.
The other reason we are looking at hobbing a worm gear is because it is an interesting learning experience and neither of us has done it before. While perhaps not strictly required for this repair, there are other applications that an ability to make worm drive gear boxes could come in handy in the future. Those electric actuators for example you occasionally see use a worm drive gearbox to gear down a DC motor.
It could be because of the effort involved to make the the hob we decide not to, in which case plan "B" will probably be a helical gear with a slight angle on the teeth (a bit over 5 1/2 degrees) to match the worm. A modified tooth form may be needed but could be done. How long the resultant gear lasts will depend on the use the saw gets and how carefully it is operated and maintained.

Michael

Hi Simon,
I wrote out a big reply then just looked at the updates on this thread and it's not here.

I sorry to see this saw is looking like not so much of a bargain and it could go up and past the price of a new Chinese saw, though it will be a better saw when fixed.
I have been tied up over the weekend, but if I had of known you where buying it so quick I would have told you to check the gearbox as it's been mentioned on many forums to at least check the gearbox as thats the main thing that wears.

What I wrote earlier was what about using a good grade aluminium? I can get aluminium plate for $11 kg so it's cheap enough.
If you made a gear out of aluminium it would give you experience and if it didn't last for a lot of years you could make one out of something else with this experience.

You have a rotary table and if you go with the fly cutter idea it would be cheap and get you going. If the gearbox is kept full of oil I can't see it wearing out any time soon.

If this was a saw I picked up and finding those prices for material, I would go this way to at least try it. It's a home shop machine so I think it will last a while.

What do you guys think?

Dave

By fly cutting, do you mean a profiled tool in a boring bar??
My interest has been sparked

Phil

Thanks for the reply Michael, that explains a lot. It's amazing the science and calculations that goes into cutting gears!

I have been looking closely at my latest acquisition with much interest, mostly because I have never owned one before or even looked at one and mine is in "semi kit" form as they must have partially dismantled parts of it to investigate the viability of repair. As it stands some of the limit switches, other switch gear and hydraulics are hanging off it. Now I have a couple of questions and I have just realised that I may need to take a photo to explain my question but I'll see how I go. When they talk about the feed rate, is the the feed rate of the saw lowering through the metal? I can't see any way of changing the band speed so I assume this is correct?

There is a mechanical gauge that looks like it should have a cable attached (similar to an older style speedo) which shows a scale of mm/min. WHere would the pickup be for something like this? I almost thinking it's from another machine?

The hydraulics pass through a ram which I assume lifts and lowers the saw as required. The hydraulic fluid seems to also pass through 2 manual flow control valves, one which is just hanging in the breeze (that has an ergonomic valve) which I assume controls the decent. The other valve is actually on one of the cutting guides, it's integral and one piece. Any ideas what that does?

Any help much appreciated!

Cheers,

Simon

Whilst i don't really disagree with any point Dave just made, except maybe that CI might be a better choice than ally at the cheap end of the material range, I would really like to see a gear hobbed just for the exercise. Like Michael obviously does, and no doubt many other do, i have a real interest in gears and how they interact with each other.

Originally Posted by Dave J

Hi Simon,
I sorry to see this saw is looking like not so much of a bargain and it could go up and past the price of a new Chinese saw
Dave

Boy Dave you really know how to take the shine of something!
Kidding! It's all good. I wanted a fixer uppa and that's exactly what I got. I still think the worst case scenario is to make a CI or aluminium gear and see how it goes. If I tart it up and add an aluminium gear I think I will at least get my money back... and some so there is no pressure. Either way, I don't really want to pay anymore than say $50 - $80 for the gear material. See how we go. If I (we) make it out of cheaper material of say CI or aluminium, I may make several.

I'm actually starting to get excited about getting it going and I'm enjoying the whole learning process with the gear replacement. Further, I can see myself cutting everything on this baby and the noisy, sparky cut off saw will end up with cob webs! I also now have a use for all those treadmill rollers if I decide to make a conveyor!

I just got to get my head around the sequence of operation with this thing and it's hydraulics. There is also a switchbox with wires that lead to the motor and a coolant hose goes in there, but no coolant hose coming out? What the? Is there a pressure switch so that the blade cannot run without coolant pressure? It's doing my head in!

Now I gotta try get to sleep with all these ideas buzzing around in my peanut.....

I'm a humming Bird!

Cheers,

Simon

I think one aluminium one will last several years, a few should last a life time as long as the oil is kept up.

As for the switch I have no idea without looking at it. I know I wired mine with a switch so I can either have coolant running when the motor running, or not running. This way the coolant switches off when the motor stops after the cut.

Did the bolts on the gearbox look like they had been undone recently? I wonder if the guy knew what was wrong with it.
Nothing worse than buying something and then finding this sort of damage.

Are you close to a H&F shop, you could always go and have a look and a talk to the service guy, maybe he would unscrew the cover of a similar one to see if the gear was similar.

Dave

Originally Posted by simonl

There is a mechanical gauge that looks like it should have a cable attached (similar to an older style speedo) which shows a scale of mm/min. Where would the pickup be for something like this? I almost thinking it's from another machine?

The hydraulics pass through a ram which I assume lifts and lowers the saw as required. The hydraulic fluid seems to also pass through 2 manual flow control valves, one which is just hanging in the breeze (that has an ergonomic valve) which I assume controls the decent. The other valve is actually on one of the cutting guides, it's integral and one piece. Any ideas what that does?

Any help much appreciated!

Cheers,

Simon

Wild guess time again! The blade speed should be able to be changed my guess is that the speedo you refer to shows the blade speed. The cable should attach to the hub of one of the blade wheels either directly or perhaps with a hat shaped bracket? (or maybe a gear box shaft) Looking at one of the photos posted of a "new" one, I'm wondering whether the speed change is done via a CVT type pulley.
When you say valve, are you meaning a 'turn the handle variable flow' type or a lever operated off/on type? On that type of saw the rate of blade decent should be controllable (variable flow) but there should also be a valve for raising the saw (probably an on/ off type but could be variable). From what I've read it is a semi automatic saw so that when the cut is finished, the saw pops up ready for the next piece of material

I may have to have a closer look. There seems to be what looks like a turn knob that tensions the toothed drive belt that connects the motor to the bearbox. I was thinking it was elaborate to have a very user friendly handle to adjust tension on the belt as I thought how often would you need to adjust that? Are you thinking that adjusting the tension will adjust the speed?

There is a small pulley down opposite the motor with nothing connected to it., it is house in a small block of steel with a grease nipple and what seems to be a small rectangular output shaft, perhaps the cable came off the back of that to the speedo?

I'll take some more photo's tonight and post.

I'm postulating on all this because I just have not had the time to really take other stuff apart. The place where I bought it from replaced this machine with the exact same brand and model. It is probably a later model but maybe I should ask to have a look and take some pics. Actually, I was talking to the guy and I made mention that he seemed to have a huge amount of steel in stock considering they build stuff "as required" and are usually one-offs. He agreed and said it's easier to store it than scrap the steel stock (eventhough they have so much stuff hanging around) because they will get bugger all for it. He went on to say that if I ever needed some steel to come see him.

Now I'm wondering if he has any bronze..........

I think I may give him a ring today.

Cheers,

Simon

Simon,

Have you looked into using an engineering plastic instead of bronze? i.e.
Metal Replacement | Solutions | Dotmar

I haven't used anything for bronze replacement but when I've needed engineering plastics I usually go to the local plastics engineering place to purchase their offcuts (at a very reasonable price).

Christian

That's a good thought Christian, the place I normally shop sells stuff called UHDP, ultra high density polysomthingarather. I asked them what it was good for, the guys said low speed high load applications, the example they used was backhoe pivot pin bushes....
I am still in the process of replacing the gear train on the mars with acetal, but of course it won't have the load on it that the bs drive gear will.
Cheers,
Ew

Hi Christian,

Not I haven't thought of a plastic metal replacement. I'm open to all avenues. Whatever material I choose, I will be making a "test" gear out of plastic first and testing it for mesh and fit. I have a local plastic fabricator that I visit for plastic sheet. They all sorts of off cuts, usually 20mm & 25mm thick off cut of Ultra High and HDPE (or is it HDPU, not sure) and it's great for many little projects. It machine beautifully as long as you keep the feed rates down, otherwise it overheats and tends to smear, affecting the surface finish.

Simon

OK. I'm starting to reduce the number of posibilities in the manufacture of this new worm gear. I just had a quote from my local steel merchant for both Bronze and Brass bar in 150 diameter.

For 100mm of 150mm Dia I'm looking at:

Brass: $400 + GST
Bronze: $450 + GST



Looks like your predictions were not far off the mark Michael!
I obviously only need 25mm of the stuff but it would still set me back over $100. Plan B

Simon

Originally Posted by simonl

I obviously only need 25mm of the stuff but it would still set me back over $100. Plan B

Simon

That if you get it right the first time, LOL

Dave

Originally Posted by Dave J

That if you get it right the first time, LOL

Dave

Exactly. That's why any gear that ends up in the gearbox will be the second one I make. The fist will be out of plastic! Anyway, making it out of new stock from brass or bronze has now been excluded. I'm not fussed, more than one way to skin a cat. It will happen one way or another, this is all part of the fun!

Cheers,

Simon