gjgm
Well-Known Member
or toolstation.com. Get plenty of sponge heads-they shred if you catch anything!
how do I slow the revs on an angle grinder - for polishing hull
- Thread starter Modulation
- Start date
LittleShip
Well-Known Member
All that hard work trying to get plastic to shine..........Ha
Buy a wood boat and paint a shine on. Ohoooo! just ducking and diving now? /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif /forums/images/graemlins/crazy.gif
Buy a wood boat and paint a shine on. Ohoooo! just ducking and diving now? /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif /forums/images/graemlins/crazy.gif
Sans Bateau
Well-Known Member
If I had wanted to spend my time varnishing or painting I would have become a decorator!
Modulation
Well-Known Member
Thanks, all
Great replies - I know now what NOT to do. I, too ,had one of those "polishers" and I'm unsure how the sellers deal with prosecutions under the Trades Descriptions Act. I have rarely come across a piece of kit which is so useless. In fact I just binned it.
I think I'll rent a low speed rotary polishing tool for a weekend. /forums/images/graemlins/wink.gif
Great replies - I know now what NOT to do. I, too ,had one of those "polishers" and I'm unsure how the sellers deal with prosecutions under the Trades Descriptions Act. I have rarely come across a piece of kit which is so useless. In fact I just binned it.
I think I'll rent a low speed rotary polishing tool for a weekend. /forums/images/graemlins/wink.gif
grimmy
Active Member
Hi, if you look in PBO (November) page 93 you can make one using a speed controller for a domestic fan. They say the cost would be about £6. I bought an angle grinder with a built-in electronic speed adjustment very cheaply from B&Q. Yes it can get quite hot if you give it some wellie but if you take it easy and let it run off load for a while every so often it works fine. I thought I would have to throw it away after I first used it but it has now seen 4 complete cutting, compounding and polishing cycles on my 9m yacht and it is still working.
VicS
Well-Known Member
[ QUOTE ]
if you look in PBO (November) page 93 you can make one using a speed controller for a domestic fan
[/ QUOTE ] I saw that but I wondered what type of fan controller would be sufficiently highly rated as to be suitable for a grinder. They are typically around 700watts for a small one or !500 watts for a large one
If any one is thinking of trying the idea they should check the max power rating and ensure that it is equal to or more than the power of their grinder.
While on the subject of the one in PBO if you look closely you will see that the wiring between the junction box and the controller has no outer sheath and that the outer sheath of the incoming power supply ends outside the junction box. It is likely to fail a safety test on both of those counts!
if you look in PBO (November) page 93 you can make one using a speed controller for a domestic fan
[/ QUOTE ] I saw that but I wondered what type of fan controller would be sufficiently highly rated as to be suitable for a grinder. They are typically around 700watts for a small one or !500 watts for a large one
If any one is thinking of trying the idea they should check the max power rating and ensure that it is equal to or more than the power of their grinder.
While on the subject of the one in PBO if you look closely you will see that the wiring between the junction box and the controller has no outer sheath and that the outer sheath of the incoming power supply ends outside the junction box. It is likely to fail a safety test on both of those counts!
philip_stevens
Well-Known Member
As Vic says, check the current load of the "polisher" before making a speed controller. I've got one of these so-called polishers, but going from a speed controller I made myself.
One that I made, I used a 1000W dimmer switch (that I just had in the junk box), on one half of a dual plastic accessory box. The other half was a single 13A socket.
The live wiring went first to the common of the dimmer, and from the 1 terminal to the live terminal of the socket. The neutral went straight to the socket terminal.
To prevent the cable being pulled out of the plastic box, I mounted it on a piece of wood, and clipped the cable to the wood with two clips.
The loading of my polisher is only 120W, so a 400W dimmer would suffice in my case.
The downside is that it gets hot quicker, as it does not have the cooling air through-put that it should have at normal speed. Every so often, just turn the speed up to full to give it a cooling blast - while giving your arms a rest! Though in the winter cold air, it is not so much of a problem.
One that I made, I used a 1000W dimmer switch (that I just had in the junk box), on one half of a dual plastic accessory box. The other half was a single 13A socket.
The live wiring went first to the common of the dimmer, and from the 1 terminal to the live terminal of the socket. The neutral went straight to the socket terminal.
To prevent the cable being pulled out of the plastic box, I mounted it on a piece of wood, and clipped the cable to the wood with two clips.
The loading of my polisher is only 120W, so a 400W dimmer would suffice in my case.
The downside is that it gets hot quicker, as it does not have the cooling air through-put that it should have at normal speed. Every so often, just turn the speed up to full to give it a cooling blast - while giving your arms a rest! Though in the winter cold air, it is not so much of a problem.
Sans Bateau
Well-Known Member
Its not so much a case as there not being enough flow through of air to cool it. If there is not enough current to spin the motor (your regulator) at design speed the windings just become a miniature heater. Dont forget you are putting a load on this motor.
Years ago when I used to sell garage equipment we had similar problems with people insisting on connecting a 3hp electric motor on compressors up to a 13amp socket when it should have been 30amp. Yes the motor turns but not as per design, then he motor burns out.
Invest a little money in the right tool to do the job.
Years ago when I used to sell garage equipment we had similar problems with people insisting on connecting a 3hp electric motor on compressors up to a 13amp socket when it should have been 30amp. Yes the motor turns but not as per design, then he motor burns out.
Invest a little money in the right tool to do the job.
VicS
Well-Known Member
[ QUOTE ]
insisting on connecting a 3hp electric motor on compressors up to a 13amp socket when it should have been 30amp. Yes the motor turns but not as per design, then he motor burns out.
[/ QUOTE ] Sorry I dont quite understand that. A 3hp motor is 2.24 kw (1 hp = 0.746kw). 2.24 Kw will draw 9.33 amps from a 240 volt supply ( 2240/240 ) so a 13 amp supply should be quite adequate provided the starting current was not too high but if that was the case it would blow the fuse and not run at all!
While Philip makes a valid point the main problem wth slowing powertools from very high speeds (small grinders run at upto 11,000 rpm) to very low ones with electronic controllers is that they end up with very little torque. You adjust the speed to what you think is right but as soon as you put load on it it slows to almost nothing. You then have to adjust the controller so that you get the speed you need under load, it remains very sensitive to the load you apply and when you remove the load it speeds up to way above that which you require. I guess that helps to overcome any heating problem but it is a nuisance if you are using a wet compouding mop because it spins all the water and compound out.
A 9 inch angle grinder BTW is about 2000 watts, a bit more than the 1500 I suggested ealier!
insisting on connecting a 3hp electric motor on compressors up to a 13amp socket when it should have been 30amp. Yes the motor turns but not as per design, then he motor burns out.
[/ QUOTE ] Sorry I dont quite understand that. A 3hp motor is 2.24 kw (1 hp = 0.746kw). 2.24 Kw will draw 9.33 amps from a 240 volt supply ( 2240/240 ) so a 13 amp supply should be quite adequate provided the starting current was not too high but if that was the case it would blow the fuse and not run at all!
While Philip makes a valid point the main problem wth slowing powertools from very high speeds (small grinders run at upto 11,000 rpm) to very low ones with electronic controllers is that they end up with very little torque. You adjust the speed to what you think is right but as soon as you put load on it it slows to almost nothing. You then have to adjust the controller so that you get the speed you need under load, it remains very sensitive to the load you apply and when you remove the load it speeds up to way above that which you require. I guess that helps to overcome any heating problem but it is a nuisance if you are using a wet compouding mop because it spins all the water and compound out.
A 9 inch angle grinder BTW is about 2000 watts, a bit more than the 1500 I suggested ealier!
Sans Bateau
Well-Known Member
VicS
Well spotted, I'm talking a load of rowlocks! /forums/images/graemlins/blush.gif
The motor was 5.5hp, 3kw single phase. This was the smallest sized compressor that would drive a HVLP spray gun (at the time, things may have changed).
On the subject of the RPM of a grinder or polisher, the head speed is achieved via gearing. As you indicate, reduce the speed of the MOTOR and it can stall and will overheat.
Well spotted, I'm talking a load of rowlocks! /forums/images/graemlins/blush.gif
The motor was 5.5hp, 3kw single phase. This was the smallest sized compressor that would drive a HVLP spray gun (at the time, things may have changed).
On the subject of the RPM of a grinder or polisher, the head speed is achieved via gearing. As you indicate, reduce the speed of the MOTOR and it can stall and will overheat.
seacomm
Member
Yes you can slow down a small angle grinder for polishing. I use a speed control from an old Hoover cleaner in a suitable box with a 13 Amp socket and a short lead with a plug on. This is rated at 1000W and will handle most small grinders.
It works well for the smaller more intricate bits on deck and neither the control or the grinder appear to get particulally hot.
I bought a E-Bay cheapie for the large area of the hull and this has worked well a bargain at £37!
It works well for the smaller more intricate bits on deck and neither the control or the grinder appear to get particulally hot.
I bought a E-Bay cheapie for the large area of the hull and this has worked well a bargain at £37!