Circular Saw stopping

[CowboyBeBop]

Hi,

I have a dewalt dcs391, which I bought recently and I've only used it to cut laminate flooring and a few pieces of wood. I'm trying to cut a 40mm worktop and the saw keeps stopping, the batteries overheat and die pretty quickly. I'm even trying to not cut the full depth and do it in 2 or 3 times.
What's most likely: a) The original blade is not good enough or not sharp anymore? b) 2.0 ah batteries are not enough? c) something else?

I only have 2x 2.0 ah batteries as I only use the saw and a combi drill very occasionally for small jobs.

 

[Bingy man]

Sounds like the battery’s are shot imo. A clue to this is how long do they take to charge and how soon are they flat . ??? Also 2 ah is not much oomph to cut 40 mm worktop even at 1/2 depth hence why this issue didn’t arise when you was cutting laminate flooring ..I stopped using dewalt for this reason - 1.4 ah ..
Edit did you purchase it new or pre owned ??

 

[Sideways]

Regardless of the wear, condition, etc your batteries are far to small to power a circ saw at full capacity.
At the least, look for a physically bigger battery with two or even three rows of cells. The rows are wired in parallel so these bigger batteries can supply 2 or 3x the current of a smaller battery and this is needed by a circ saw.

 

[Richard_C]

The ah number is a measure of capacity, not power. Think of it as a car with a small petrol tank - you have to fill it more often but it has the same power as one with the same engine and a bigger tank. Some bigger capacity batteries will deliver current more quickly but not all.

I think blade is most likely, and it's the least expensive thing to change. Cutting laminate flooring can be harsh on blades regardless of saw type, probably a combination of resins and plastics but I have found it blunts blades quickly. Also there is no perfect do everything blade. The 3 variables are diameter and bore, which are determined by the fit of the machine you are using, and the number of teeth. A fine blade is likely to struggle in thicker work as it can't clear itself well, plus if its a bit blunt and gets warm in things like a worktop it all gets a bit sticky. I would invest in a new blade and see what happens.

I was about to give up on my sliding mitre saw, a cheap Titan one, on which I had cut quite a lot of laminate flooring, but a few ££ on 2 new blades, a fine and a medium coarse for different jobs, and I had a good as new machine which works very well.

 

[Jameshow]

Regardless of the wear, condition, etc your batteries are far to small to power a circ saw at full capacity.
At the least, look for a physically bigger battery with two or even three rows of cells. The rows are wired in parallel so these bigger batteries can supply 2 or 3x the current of a smaller battery and this is needed by a circ saw.

I wondered how this could be...that explains it.

 

[Adam W.]

It's Volts that counts with a saw, not amps. Amp hours is just a measure of how long the battery will deliver the volts.

If you want to cut 40mm stuff a 36v saw is what you want. 18v saws are for ply, OSB and roof battens.

 

[Ozi]

Do you have a jig saw? When cutting counter tops a nice new blade and my 25 year old Bosch whistles through, first hint of slowing of burning and change the blade keep the old blade for rough stuff.

 

[CowboyBeBop]

Thank you for your answers. A few comments:

• I'm a casual DIYer faced with a task I don't expect to encounter often.
• I opted for Dewalt, but I could have chosen Makita or cheaper brands. I don't believe this is a brand issue, and I don't want to spend a couple of hundred pounds changing the two tools and batteries I have.
• This is a sort of entry-level circular saw that suits my skills and needs.
• I also don't need or have space for more powerful tools at the moment.
• @Richard_C, thanks for your sensible answer. Do you, or anyone else, have any blade suggestions for this and for any solid wood cutting in the future? I'm also planning to build a plywood closet in the future, so any tips for good blades for plywood would be appreciated.
• @Ozi, I was going to buy a jigsaw, but I managed to finish installing a new laminate floor without it, so for now, I'll postpone that purchase for a bit later. Thanks for the info, though.
  
  

 

[TheUnicorn]

from Do Battery Amp Hours Affect Power? | 2.0Ah vs 5.0Ah

BATTERY AMP HOURS AFFECT POWER, BUT WHY?​

It stands to reason that if both battery packs deliver 18 volts, it shouldn’t affect the power, just the runtime. A closer look at the pack design offers some insight. Power is measured in watts and you can calculate it by multiplying volts and amps.

The drill really is asking for 18V from both batteries, so that remains constant. Where the number of cells comes into play is in the amps (current). Let’s say the Makita XFD07 needs 360 watts of power to drill the next hole. At 18V, the batteries each need to deliver 20 amps of current to make it happen (18V x 20A = 360W).

Each cell in the series has to contribute the full current since it isn’t additive between series connections. The 5 cells in the 2.0Ah pack each need to deliver 20 amps. In the 5Ah battery, there are two sets of cells, and the parallel connection between them does make the current additive. So each set only asks its cells to give 10 amps each.

It’s much easier for 10 cells each working half as hard to keep the power level up. The tougher the task, the harder it is for 5 cells to maintain the same power level as 10 cells.

It’s a similar story when you test runtime. In theory, a 4.0Ah battery should give you exactly twice the runtime of a 2.0Ah battery. However, you actually get a bit more than that. We found that amp-hours affect runtime in a big way.

 

[cally60]

I have the same model Dewalt saw, and had the same problem. I found that a 4ah battery solved the problem.
For some reason the smaller batteries don’t have enough grunt

 

[Doug71]

I's probably a combination of blunt blade and too small batteries.

I have some 1.5ah & 2ah18v Makita batteries for my drills and they are designed to not fit some of their higher draw tools (unless you adapt them ) as they don't have enough oomph.

Does that saw have a riving knife, if not the cut could be closing up and be binding on the back of the blade.

If you are cutting along the grain in solid wood you want a blade with a low tooth count.

 

[cally60]

I should have read the Unicorn’s post more carefully!

 

[cally60]

If it’s the original blade that came with the saw, you will get a lot more work out of it than stated in your OP.
I would replace the battery with a min 4ah version, before looking a replacing the blade.
It solved the problem for me

 

[worn thumbs]

First of all,take a really close look at the blade tips,it you can see a band of light reflected the saw isn't sharp enough.A blade will almost certainly cost less than a new battery or your local sharpening specialist might be able to give it a new lease of life for less still.Is the blade the optimum type for the work you are doing as far as tooth numbers are concerned?I've seen a 3 phase saw struggle with 18mm ply because it was fitted with a 96 tooth triple chip blade.Only when you have a sharp blade of the correct variety will you be able to make informed decisions about batteries.As said above,AmpHours is a measure of endurance rather than outright power.

 

[Phil Pascoe]

Have a look at TCT Circular Saw Blades | Saxton Blades

Half decent blades that aren't too expensive. Not up to professional heavy use but perfectly adequate for most of us.

 

[CowboyBeBop]

Thanks guys. Really helpful. I think it can be a combination of the two.

For my future project, clean cuting plywood, what blade would you recommend? And would that blade work for this as well or should be a different one?

 

[AESamuel]

Larger amp hour batteries absolutely provide more power to the tools.

Yes, in an ideal world two 18v batteries would both deliver 18 volts regardless of capacity, but voltage drops as batteries discharge, meaning a larger battery keeps a higher voltage for longer. That and the current draw being spread across more cells as in @TheUnicorn 's post means bigger batteries = more power.

Check out some of the videos on YouTube comparing battery capacities - it makes quite the difference!

 

[Phil Pascoe]

Thanks guys. Really helpful. I think it can be a combination of the two.

For my future project, clean cuting plywood, what blade would you recommend? And would that blade work for this as well or should be a different one?

A 40T or 60T. I use an 80T, but some find them a bit too fine.

 

[pe2dave]

It's Volts that counts with a saw, not amps. Amp hours is just a measure of how long the battery will deliver the volts.

If you want to cut 40mm stuff a 36v saw is what you want. 18v saws are for ply, OSB and roof battens.

I beg to differ Adam. The water analogy makes this clear.
Power is a combination of voltage and current, see other comments.

 

[Etaf]

i used a Sliding Mitre saw to cut a lot of laminate flooring when you doing a ground floor of a house
We had a silverline 250mm 60T blade , and it lasted about 8 cuts - pretty useless on laminate
i read the posts and didnt see what blade you are currently using and just how much flooring did you cut

I changed over to useing a freud blade and it worked much better and lasted much longer
However, Now i use saxton blades - they are the almost the same price to buy as get the Freud blade sharpened
use the saxton blades in SMS and also in regular circular saw (which i also had a freud blade for)

I have also used a 2AH battery on the Circular saw and it does have trouble , even with 18mm MDF - changed to use a 5AH and much better result