Last months PBO - Angle Grinders

[andy_wilson]

This must be about the last power tool in my cupboard I would think to use on my boat.

But the bit about slowing it down using a 'fan speed controller', and using it as a polishing machine struck a cord, until I gave it a second thought.

My Makita has a proud boast on the manufacturers web site - "Jobsite Proven for Over 20 Years".

How long do you reckon the motor would last run at 500 rpm spinning a large polishing bonnet, rather than the 10,000rpm design speed.

I think that little bit of the article was as ill thought as the plank of wood with the said controller and ancilliaries, given the outside nature of the work, and the fact that polishing normally involves adding water too.

 

[Boathook]

The angle grinder is very handy for the correctly chosen job on a boat. Another tool is the dremel.

 

[Talbot]

I have used an angle grinder for a lot of tasks onboard. I also have a proper sander/polisher style angle grinder, which runs slowly enough for polishing.

You can purchase a cheap version of this from here code 868663

 

[rogerthebodger]

The one big thing that was not covered in any way is that all power tools are over powered and when used heat up to a greater or lesser extent.

If you buy an industral motor which is "continous rated" it will run all day every day at max power.

All power tools have a "duty cycle" There is a period it can run and then it must have a cooling period.

10% duty cycle means only 6 minutes use in every hour and if you use it more it will burn out.

Now as the cooling is effected by a fan driven by the motor running at the motor speed, the cooling air flow which cools the motor reduces as the speed is reduced and there must effect the duty cycle as the motor will heat up quicker and only cool at the same rate

I had 2 Makita die grinders with built in variable speed 6000- 30000 rpm. I did some stainless polishing using flap wheels at 12000 rpm (flap wheels rated at 15000 rpm. The die grinders burnt out twice in 3 mins of operation.

Running with grind wheels rated at and running or full speed (30000rpm) I could work all day no problem.

I had to buy die grinders running at 1000 - 6000 rpm for that job to get the cooling to the correct level to have a usefull duty cycle.

Have tried to get duty cycle info from Makita in Germany and had no joy to date.

I think the guy who wrote the article may know how to sell power tools but he does not know how they are designed or use then in a realistic way.

I do not use power tools in my job but as a hobby in building and improving my boat like most involved in boating do who read and subscrive to PBO (PRACTICAL boat owner)

 

[oldsaltoz]

G'day Andy,

I have a range of 5 angle grinders, 2 die grinders and 2 drills used every day on fibreglass. Each grinder, die and drill has it's own attachment and each is rated to operate the different types of attachments. Diamond faced cup grinders, flexible grit faced concrete grinder, diamond edge cutting disks, and diamond tipped hole saws to name but a few.

I still manage to burn one out from time to time but they each do a lot of work before showing any sign of failure.

Reducing the speed of any power tool by reducing the power supply almost certainly kill it, if not the same day then shortly after depending on how long or hard it's worked.

Having the 'right tool' for the job makes it faster, safer and in the long run less expensive.

The angle grinder is one tool that is available in wide range of speeds, power and work ratings, using an underpowered unit can work out very expensive so purchase a good one or hire one if you can not afford to buy the quality you need.

Andavagoodweekend......

 

[fishermantwo]

[ QUOTE ]

The angle grinder is one tool that is available in wide range of speeds, power and work ratings, using an underpowered unit can work out very expensive so purchase a good one or hire one if you can not afford to buy the quality you need.

Andavagoodweekend......

[/ QUOTE ]

Oldsaltoz,
If you have an ALDI shop close by, keep an eye out for their specials on grinders. Their 115 mm grinder is a pearler. I generally destroy a couple of grinders a year, does not matter what brand. Their grinder made by craft costs about $20, lasts really well and unlike others is easy to pull apart. I notice its popular here with other fishermen too.
The only problem is the special only appears a couple of times year and you may have to elbow a couple of pensioners out of the way to get to them.

 

[oldsaltoz]

G'day Andy,

We do have ALDI shops here but only the Supermarket type I think, and certainly not close to me, living on the mid east coast puts me over 1,000Km from Brisbane or 2 hours on a jet, so not an option.

Do they have any brand name on them or info on power rating, RPM etc?

Avagoodweekend......

 

[boatbuilder]

I use a lot of air tools , cheap , and they dont burn out. /forums/images/graemlins/smile.gif

 

[oldsaltoz]

G'day boatbuilder,

Yes we use a few air tools too' 3 spray guns, 2 sanders, small grit blaster, duster, tyre gauge/inflator, and degreaser. Single phase belt driven compressor.

We are now getting more and more cordless equipment, no leads or hoses to run, no power required, handy when working on building sites with lots of competition for a few outlets. most are down a little on total power / grunt or RPM but still save time and improve safety.

Avagoodweekend......

 

[Lakesailor]

I use angle grinders to cut steel, grind welds, strip paint with a twist wire brush. I've used 3 angle grinders in 5 years. At £15 each from Homebase that seems like good value. When you look at the "Pro" models at £90 you think "How long would they last then?" Not 30 years I'll bet.

 

[DepSol]

I use a Rupes grinder for polishing all day long, I never run it at 500rpm more like 2000 rpm. It all depends on how you use it and how much pressure you apply.

These machines have lasted me years when combined with the right materials ie a proper head and bonnet, I use 3M hookits, it will last ages provided that you get rid of any fluff in the cooling fins.

Admittedly some grinders don’t last but as I say I have 3 Rupes machines and the only thing to break on them was the lead when my mate had it wrap around the head as he wasn’t paying full attention.

Jake Kavanagh who wrote the article isn’t a salesman and he has been shown the merits off using a grinder as a polisher from someone who knows what he is talking about and has shown people at Sunseeker, Fairline, Princess to name a few companies how it should be done.

The only criticism I can give to that article is that he missed out the use of XL wheels and how well they clean up shafts and propellors.

 

[oldsaltoz]

G'day Phil (LakeSailor),

I'm sure even the most expensive would not last 30 years even with domestic cycle use. The sort of use I'm referring to where a better quality grinder is better value for use every day, and I mean every day and for more than a few minutes.

Just transporting, handling onto and off a job site then transporting to the next job every day is enough to kill some of the cheaper ones, drop it a couple of times and it's all over for some.

I carry at least 5 grinders with me every day, each is fitted out and ready to go, I hated changing attachments on the job so invested in more grinders; each grinder is rated depending on what it's prime use, the one with the diamond tipped cup grinder is the top of the range, it may have to run for a couple of hours at full load on compressed fibre cement sheeting, hard work for any grinder and a killer for cheap ones.

I also use a top of the range grinder to remove gelcoat or fibreglass when required below the waterline of a hull, the disc is a designed to grind concrete so makes short work of glass fibre and resin but takes a bit of getting used to. It takes me less than a day to remove the gelcoat below the water line on a 30+ footer and I'm not killing myself or the grinder. a single will do at least 3 hulls. Again a cheap grinder will not stand up to the loadings or the high dust and grit flows.

I do use some less expensive lower rated grinders for cutting off PVC waste pipes and cutting aluminium angles etc.

I hope this helps.

Avagoodweekend......

 

[rogerthebodger]

It's like all tools "buy the right one for the job". The I wanted to make is if you know the designed duty cycle you have a better chance of picking the correct power tool for the job.

I too have a number of angle grinders and other power tools both 110 mm and 230mm (2000+ watt) for realy heavy jobs down to the cheep 150 ZAR (10 quid) for deburing cut steel and different makes / rating in between.

The other point is that most power tools are not designed to run for more than 2 - 3 mins at anything below full speed. Electronic variable speed tools are c**p in my view and this guys use of a variable speed unit is IMHO irresponsible and until a tool manufacturer comes up with real duty cycle data to disprove my view

 

[DepSol]

My Rupes are all variable speed which is required as Compounding uses a different speed to Polishing and depending on the condition and temperatures those speeds vary slightly too. As I said the Rupes are robust enough and can last all day every day.

I think this was a good article in general. I use a cheap B&Q one with XL wheels for metal but aprt from that it’s the Rupes every time as some others I have tried don’t last 5 minutes. Saying that the Rupes aren’t cheap but worth every penny as the return I get from them is well worth it.

 

[Guest]

Cheap vs Expensive ...

I agree that Pro versions ... I mean TRUE Pro versions - not the price inflated stuff at DIY shops - are sensible if a lot of work is anticipated.

But for average person who uses it occasionally ? I have a £6 chinese job with quick-fit system etc. takes about 6" diam. discs ... to be honest - it accepts all discs that can fit within safety guard ... That has plugged away for last year on various stuff .. and performed well.
My thought is that if it lasts a year ... get another ... money saved is considerable against "Pro" version ... which given my luck would probably not last much longer anyway !!

I have a system with tool-kits .... the multi-jobs available at Makro / B&Q etc. Yes the tools included are cr*p and break quite easily ... so as they break buy better that fits the cut-out in the box .. meaning you have a decent carry-unit with ever increasing good tools in ...