Crazy (Christmas) Project - Belt Sander

[wobblycogs]

Many many thanks Bob. I'll bear that in mind when deciding whether to go ahead with this particular project. I actually have three phase power to the house it's just that because of the state of the place I can't get three phase to my current workshop (a first floor bedroom).

What I'm currently thinking is this: get a big inverter (3kW say) and a 0.55kW three phase motor for the belt sander project. When I move to my real workshop in the cellar I'll run in three phase power and use that directly on the belt sander freeing up the inverter for use on the bandsaw - if I understood your motor document correctly an inverter is needed for variable speed.

I think the inverter has a RS485 port which can be used to program it. I'm on much more familiar ground with programming, I wonder if I could knock something together that allowed me to switch programs at the touch of a button... project for another day I think. I hear what you are saying regarding the plug and socket though, will have a think about whether it's worth the risk.

What I lack in skill I try to make up with enthusiasm and lots of reading. I should have become an engineer rather than a programmer - it's far more exciting building things in the real world.

 

[9fingers]

Many many thanks Bob. I'll bear that in mind when deciding whether to go ahead with this particular project. I actually have three phase power to the house it's just that because of the state of the place I can't get three phase to my current workshop (a first floor bedroom).

What I'm currently thinking is this: get a big inverter (3kW say) and a 0.55kW three phase motor for the belt sander project. When I move to my real workshop in the cellar I'll run in three phase power and use that directly on the belt sander freeing up the inverter for use on the bandsaw - if I understood your motor document correctly an inverter is needed for variable speed.

I think the inverter has a RS485 port which can be used to program it. I'm on much more familiar ground with programming, I wonder if I could knock something together that allowed me to switch programs at the touch of a button... project for another day I think. I hear what you are saying regarding the plug and socket though, will have a think about whether it's worth the risk.

What I lack in skill I try to make up with enthusiasm and lots of reading. I should have become an engineer rather than a programmer - it's far more exciting building things in the real world.

I wondered if you were a programmer when you numbered your questions starting with zero!!

You should be able to block download parameters via the 485 port. You already have a manual so you might be able to judge how easy that might be.

Most inverter manuals are written by people who are highly familiar with their particular inverter and often over look some critical item of info that they know and is obvious to them.
A bit like programmers writing software manuals! :lol:

One possibly flaw in your future inverter plans. Inverters are either 240 in/240 out or 415in /415 out (although there are some now that are 240 in 415 out).
Currently you need a 240 in 240 out inverter for your sander, so when you run your three phase bandsaw from the inverter, it will have to be a dual voltage motor and the inverter will still have to be connected between one phase and neutral.
The ebay listing for the inverter is confusing where is says the input can be single or three phase.

hth

Bob

 

[wobblycogs]

Ok, I've just read your post three times and it's now clicked that the problem is. If I buy a dual voltage motor for the sander and the bandsaw I think I've got all angles covered. When the sander is on the inverter it will be in 230V configuration and when I move the sander to be directly powered off 3ph I can switch it to 415V configuration.

From what I've read I'm not convinced that the inverter can actually take 3 phase input. I suspect that is one of a multitude of mistakes in the listing. I'll have to dig through the 70 pages of badly formatted and translated manual to find out for sure. If it can I can't find anyone that has wired it up that way.

I've not been able to find a 230 --> 415 inverter and as you say they are probably quite expensive at the moment. All things considered I'd rather make everything that is going to have a 3ph motor run be able to run at 230V as it's highly unlikely I'll be living here forever and it was a fluke that we bought a place that had 3ph fitted (the house was bed sits and all heating and cooking was electric hence the need for loads of power). Who knows though maybe I'll fall in love with this house one day.

 

[wobblycogs]

Ok, so I bottled it and went with a 1HP single phase motor I found going fairly cheap and most of the other parts have arrived now too . The springs I received from ebay are the wrong type (tension rather than compression) and the guy's not responding so that could cause a hold up. I also haven't got a v-belt yet as I don't know the final distance between centres for the pulleys.

I do, however, have one quick question about motors. Is it possible to run them at any angle or do they have to be upright? The motor I have is foot mounted with box containing the capacitors on top. This makes the motor quite tall and it would improve the design if I could have the motor mounted on it's side.

A word of warning to anyone thinking of making one of these - don't bother unless you are doing it for fun as it would have been a lot cheaper and simpler to just buy one :lol:

 

[Chems]

If your going to all the trouble why not make a full sized wide belt sander

 

[9fingers]

I do, however, have one quick question about motors. Is it possible to run them at any angle or do they have to be upright? The motor I have is foot mounted with box containing the capacitors on top. This makes the motor quite tall and it would improve the design if I could have the motor mounted on it's side.

You can run motor in any attitude. Make sure that you do not obscure any vents and if you have an older style motor with openings through to the windings, make sure debris cannot fall or get sucked into the windings & bearings.
Modern TEFC (totally enclosed fan cooled) motors look after this problem and are superior to open frame motors.

hth
Bob

EDIT: many TEFC motors allow the mounting feet to be bolted on in different positions which normally allow the capacitors to be either at the side or on top with respect to the feet. Somtimes the holes are ready tapped or other times they are cast in but need tapping typically M8

 

[wobblycogs]

Champion, thanks for that Bob. I hadn't noticed the feet could be moved as everything is painted a very dodgy orange colour. I've got a TEFC but I plan on taking extra care to make sure dust doesn't get near the motor anyway.

 

[9fingers]

I'm not saying all TEFCs allow this but many do. look for cast in bosses in between the fins every 90 degrees round the casing

such as in figure 4 here http://homepage.ntlworld.com/bob.minchin/Induction motors - Issue2.pdf

Bob

 

[wobblycogs]

Sorry, I didn't make myself very clear. I've already checked out the motor and the feet can be moved. It's clearly been painted after the feet were bolted on because literally everything on the motor is orange: case, nuts, bolts, washers etc. Because of the paint job I missed the fact the feet were bolted on, I had assumed they were cast as part of the body. I'll need to get some taps though by the looks of it as I don't think the holes are threaded - cheap Chinese motor . Thanks again.

 

[9fingers]

You 'might' find that the screws are self tapping that hold the feet on rather than buy taps??

Bob

 

[wysong]

As Kirk has pointed out the belt tracking is the hardest part to
adjust , your tracking adjustments has to be available to you
not hidden in the machine , the belt will never have a chance of staying on
it take split second adjustments , depending on what your sanding
and where on the belt your working .

The first picture here is of the mechanism of the belt side for a
General 100 Sander (similar to Kirks PM 30 ) the belt size is
6" by 60" , disk is 16"

the second picture is the actual machine
which is simlar to the Wadkin version

you can see in the second picture , this is the tracking adjustment
for the belt , a slight turn with the belt running sends it either way
the outside of the roller is pined , and the adjustment is on the inside
of that roller .

Hey Kirk , found ya over here too.

 

[wobblycogs]

Cheers, I've partially re-done the design and I'm about to start cutting out the pieces. the tracking knob is a little obscured but I can open it up a bit and if necessary I could probably alter the design to put it on the outside. The tracking adjustments shown in those two pictures are almost identical to the design in the only other home made (wooden) sander I've seen.

 

[9fingers]

So the medication is not really working yet then? :lol:

Bob

 

[wobblycogs]

Nope, in fact I think it's caused the problem to get worse. The prospect of maybe becoming unemployed in the new year is the only thing that will slow my machine building frenzy down I think. I'm currently trying to make enough space in the workshop to lay an 8x4 sheet of MDF down for the first cut. The workshop is, as always, a right bleedin' mess so I will probably only get that one cut done today.

 

[9fingers]

The prospect of maybe becoming unemployed in the new year is the only thing that will slow my machine building frenzy down I think.

Lets hope the job keeps open for you! Good Luck

Bob

 

[wobblycogs]

Thanks for the support regarding the job. It's actually rather worse than perhaps I made it sound. I'm a one-third owner of the company and we've just found out that we will be losing two of our biggest clients as they are trying to cut costs. Not the worlds greatest Christmas present but we aren't quite down and out just yet, cross your fingers for me.

Anyway, on with the project. I've now cut all the pieces out of MR-MDF. I hate working with MDF, It seems no matter how much extraction I've got going the dust still seems to go everywhere. A problem not helped by the fact I did a lot of the cutting with a jigsaw and a SCMS which are impossible to collect dust from effectively (IMHO).

The first cut, I only include this because it shows off the track saw attachment I made a while back. It's proved to be surprisingly accurate and useful. I've decided that one day I have to save up for the real thing.

Next was marking out. I went for the straight edge and knife approach. I managed to arrange it so that all the parts fitted into a piece of MDF 1220x725. This doesn't include any tables or stops which I'll be making separately once I've proved that the machine generally works.

Finally after a couple of hours turning the workshop green we have all the parts cut

I'm not over the moon about my level of accuracy on a couple of the parts (unfortunately the larger ones) but the parts that I think really matter I ganged up and cut in one pass so I think I'll get away with it. The one thing that is concerning me is drilling the holes for the bearings. They have to be pretty much bang on perpendicular to the fact of the MDF but I don't have a pillar drill. I'm thinking I'll probably make up a jig and route them.

 

[wobblycogs]

Ok, sorry for the lack of updates to anyone following this build. I've been rather ill over Christmas but I've still managed to shuffle out to the 'shop now and then and make some progress. I decided to set up a new website to document my wood working exploits so you can find the intermediate steps with loads of photos here:

http://www.wobblycogs.co.uk/index.php/projects/belt-sander

I've got the sender to the point where I can run a belt around the two rollers as seen bellow:

I haven't fitted the tracking mechanism yet, that should go in tomorrow - it needed a bit of a rethink. The tensioning mechanism works well but I think I'll need a third spring. There is a little bit of vibration from the primary sanding wheel, I must have done a poor job of turning it! I think I'll probably sand it round in situ so it's perfectly balanced. The crowning on the wheels works really well but there is too much crown so I'll also remove some of that. Really though I just need to fit the platen and any other tables / fences I want and I'm good to go.

Quick question: when I first started it the motor ran slowly, probably half the speed it should have. After about 30 seconds of running it burst into life and ran at it's expected 1300 rpm. It's very cold in my shop and I think the slow running was because the belt was cold and stiff and causing a lot of additional load on the motor. Once it had been running for a few minutes the belt was slightly warm (25 deg maybe? - hard to tell but certainly not hot) and much more flexible and the motor always got up to full speed in <0.5seconds. Do belts get slightly warm when running? Does a cold stiff belt sound like the right diagnosis?

I've also got a little 30 second (2.5MB) video of it running if anyone is interested:

http://www.wobblycogs.co.uk/images/projects/belt-sander-first-run.m4v

Merry Christmas everyone.

 

[tisdai]

A biggg well done m8 =D> , that is looking spot on. I like the little vid of it working,

Cheers for sharing

Dave

 

[9fingers]

Very impressive Graham!
I suspect that you are correct in blaming the temperature for the slow start up although it could possibly be the wrong type of motor providing insufficient torque. However the fact that it does reach synchronous speed eventually does point to being either underpowered or belt/temperature issues.

A belt drive is not 100% efficient so yes this wasted power does come out as heat in the belt and the pulleys.

If the machine continues to be a slow starter when the weather is warmer then you do need to sort it out. 25 seconds for the starter winding to be powered up is too long and might eventually lead to the magic smoke escaping.

Good luck

Bob

 

[wobblycogs]

Thanks again Bob, looks like it's just that the belt was cold. After a freezing night in the shop I brought the machine into the living room for a hour or so to warm up and on first starting it got up to speed in <1second. I'm pretty confident that the motor is powerful enough at 750W (commercial machines using this belt size seem to be around 500 to 600W) and it's a cap start, cap run motor so it's got a decent starting torque. By god it's got heavy quickly though - it must weight about 25kg and there are still bits to add.