Topics

Table Saw


qmp211
 

Having spent hundreds of hours testing most all of the hobbyist tablesaws and designing/building/manufacturing a small radial arm saw, I respectfully disagree with some of the opinions expressed about what will yield the best results for cutting most anything including freight cars whether plastic or wood.

IMHO I think you will achieve far superior results incorporating the following ideas.

You'll need about a 4" diameter blade to clean cut most car bodies. The most reasonably priced saw is an older, OOP Dremel Table Saw. They bring a premium dollar on ebay. Make sure you have a seller with a return policy if the saw is bent or damaged. The saw was much maligned but when it is fine tuned, it is the most versatile table saw available for the money. If you're not familiar with setting up a table saw, grab a book featuring table saw tuneups and apply the same principles.
 
The saw will need a speed controller (with the Dremel Saw, it is mandatory!!) to prevent melting of resin/plastic cars. I've never found a saw that will make these cuts without a speed controller. The Dremel cuts best at about 3450 rpm = about 1/3 speed.

What you're looking for blade wise is a jewelers slotting saw, .025" to .032" thick with ZERO set of the teeth. A high quality slotting saw is a must and will yield a superior cut with a very smooth edge. Any set will defeat your objective. Set will cause the blade to grab the part, sling it into the wall and make you count your fingers 3x's before you exhale....

The car will need interior bracing and probably a part sled to keep your fingers out of the rotating machinery. Playdough, artist putty will work. You need to dampen part vibration during the cut to prevent the blade from grabbing the car sides and making a chipped edge.

The most difficult step is getting a square, plumb cut. Just because you get a .025" kerf doesn't mean you will get to slap pieces back together without fitting and sanding. I've had the best results using a NWSL True Sander with some custom sanding blocks. Best practice is to cut long and sand back to the line.

I would avoid any full size saw even if you have the testicular fortitude to dabble. They're too dangerous.

Good luck.

Randy Danniel







Dennis Storzek
 

Here is the ultimate saw for modelwork... but try and find one!


These were designed to cut lead Line-o-Type slugs, and sheet lead for spacers to compose newspaper pages. The guy in the first video hasn't figured out that the scale is marked in Pica.

Dennis Storzek


Nolan Hinshaw
 

From: "destorzek@... [STMFC]" <STMFC@...>
To: STMFC@...
Sent: Wednesday, April 26, 2017 7:46 PM
Subject: [STMFC] Re: Table Saw

Here is the ultimate saw for modelwork... but try and find one!
https://www.youtube.com/watch?v=LfGN6Wb1ZvY
I like the micrometer-like adjustment for the fence.

https://www.youtube.com/watch?v=q2aZZLCrW9w
Too many distractions! My mind is overflowing with ways to cobble
something like that up for my own shop...
--
Nolan Hinshaw, San Francisco
"Not only is it not right, it's not even wrong!"
From Wolfgang Pauli, perpetrator of the Pauli Exclusion Principle









These were designed to cut lead Line-o-Type slugs, and sheet lead for spacers to compose newspaper pages. The guy in the first video hasn't figured out that the scale is marked in Pica.

Dennis Storzek


spsalso
 

Randy,

The whole point of set is to have the teeth cut a slot that is wider than the body of the blade.  This will minimize rubbing the surface of the cut.  And thus lessen heat generated by the friction.  Which would melt plastic.

So, I'm at a loss that you are proposing a blade with no set, which will then allow the face of the blade to rub on the plastic.  And cause it to melt.  From the ensuing friction.  And, in addition, provide more surface for the plastic to "grab".

Am I missing something here?


Ed

Edward Sutorik


Jon Miller
 

On 4/27/2017 12:46 PM, Edwardsutorik@... [STMFC] wrote:

Am I missing something here?

Don't have any experience with any of this but maybe speed of the blade, RPM.  A very slow blade speed should cut without generating heat and maybe a cooling fluid would help.

-- 
Jon Miller
For me time stopped in 1941
Digitrax  Chief/Zephyr systems, JMRI User
NMRA Life member #2623
Member SFRH&MS


spsalso
 

Jon,

I agree with both your points.  But I'm saying why not minimize or eliminate the problem by lessening blade contact by having set on the teeth.  

It just doesn't make sense to rub plastic on a spinning steel surface, which is what happens when there's no set on the blade teeth.


Ed

Edward Sutorik


John F. Cizmar
 

The some blades have a negative  "set" on some of the teeth to allow the chips someplace to go and not overheat the work.
John Cizmar  



From: "Jon Miller atsfus@... [STMFC]"
To: STMFC@...
Sent: Thursday, April 27, 2017 3:38 PM
Subject: Re: [STMFC] Re: Table Saw

 
On 4/27/2017 12:46 PM, Edwardsutorik@... [STMFC] wrote:

Am I missing something here?
Don't have any experience with any of this but maybe speed of the blade, RPM.  A very slow blade speed should cut without generating heat and maybe a cooling fluid would help.
--
Jon Miller
For me time stopped in 1941
Digitrax  Chief/Zephyr systems, JMRI User
NMRA Life member #2623
Member SFRH&MS



Scott H. Haycock
 

Steel woodworking blades of this type (no set) are hollow ground on the sides of the blades just for this reason. The thickness of the blade is reduced between the teeth and the center of the blade to eliminate the blade rubbing against the work.

Scott Haycock


 

Jon,


I agree with both your points.  But I'm saying why not minimize or eliminate the problem by lessening blade contact by having set on the teeth.  

It just doesn't make sense to rub plastic on a spinning steel surface, which is what happens when there's no set on the blade teeth.


Ed

Edward Sutorik



Dave Sarther
 

In my experience (of cutting aluminum siding) I would use a plywood blade put in the saw reverse of the way it would be installed for cutting wood.  Not certain if that would work for plastics however.  SLOW blade speed and a fast stroke seems to be the most effective way of preventing melting. 

Later,  Dave S. 


-----Original Message-----
From: Edwardsutorik@... [STMFC]
To: STMFC
Sent: Thu, Apr 27, 2017 2:06 pm
Subject: Re: [STMFC] Re: Table Saw

 
Jon,

I agree with both your points.  But I'm saying why not minimize or eliminate the problem by lessening blade contact by having set on the teeth.  

It just doesn't make sense to rub plastic on a spinning steel surface, which is what happens when there's no set on the blade teeth.


Ed

Edward Sutorik


Dennis Storzek
 




---In STMFC@..., <Edwardsutorik@...> wrote :

Randy,

The whole point of set is to have the teeth cut a slot that is wider than the body of the blade.  This will minimize rubbing the surface of the cut.  And thus lessen heat generated by the friction.  Which would melt plastic.

So, I'm at a loss that you are proposing a blade with no set, which will then allow the face of the blade to rub on the plastic.  And cause it to melt.  From the ensuing friction.  And, in addition, provide more surface for the plastic to "grab".

Am I missing something here?
======================


Set provides clearance, but typically the way the teeth are ground on cheap blades yield a rough cut surface. What Randy is proposing is a smooth side blade, that runs slowly enough (note he mentions a speed control) that it doesn't generate enough heat to melt the plastic. I tend to agree. IF your set-up is rigid enough a blade with zero set should pass through the kerf without rubbing... but that seldom happens, since the plastic parts tend to wiggle around as they heat up. The key is to keep the heat out of the work.

Dennis Storzek


spsalso
 

Interesting about the "hollowground" blades.  

I've been using "standard" carbide saw blades, and have had no problems with them.  The carbide teeth are always wider than the blade, thus making set.  I do tend to spend a fair bit on a blade, though.

Here's the type, though I haven't used this one, yet:




Ed

Edward Sutorik


Scott H. Haycock
 

In carbide blades, it's the "Triple Chip Grind" that produces the smooth cut. This is the carbide version of the " Hollow Ground Planar" steel blades I previously described.

You'll also find that the face of each tooth is ground at a negative angle so it doesn't grab the top surface of the material being cut.

Scott Haycock


 

Interesting about the "hollowground" blades.  


I've been using "standard" carbide saw blades, and have had no problems with them.  The carbide teeth are always wider than the blade, thus making set.  I do tend to spend a fair bit on a blade, though.

Here's the type, though I haven't used this one, yet:




Ed

Edward Sutorik



qmp211
 

Responses to issues raised.

A Linotype saw might be a nice saw to own. It’s the saw design that makes it great. Sliding table saws are the best way to cut most everything since the cut off falls away from the blade. For all intents a sliding table saw must be precision made. A used Linotype saw comes with incredible potential for parts no longer manufactured. Do you want to rebuild a saw or build models? FWIW, we designed and manufactured a replacement aluminum plate saw top including the sliding table on linear bearings for the Dremel saw and it’s great but we couldn’t make the price point work. 

A jeweler’s slotting saw is a precision tool designed for metal working machines,  mounted in precision arbors. They come in various stages of quality. We sold hundreds of 4” slotting saw blades for the Dremel saw custom made for us on a $350K Swiss saw blade grinding machine. They were ground round, ground flat, had precision uniform ground teeth and were made with no set in the teeth. There is no comparison between saw blades manufactured for conventional table saw blades vs. precision slotting saws. All of the saw blades we sold included two precision flat ground stabilizing washers to keep the blade running true, especially the .025” blade.

The Dremel table saw out-of-the-box was not a good product. It had terribly poor blades that had no value to hobbyists or serious modelers and when used in our applications, were dangerous. The sewing machine motor screams at 10,000 RPM. 

It takes work to make the saw do what you want.  And it will do that very well as long as you use a speed controller, use a machinist or drafting square for set-up, extend or replace the miter gauge, extend or replace the fence, use a zero clearance throat plate when needed and add dust collection. You can use the jeweler slotting saw blades for precision work or Micro-Mark’s Japanese made carbide tipped blades and get superior results for the dollars you spend. Add a couple of bicycle wrenches for the arbor and arbor nut and you’re all set.  I’ve found a zero clearance throat plate to be absolutely imperative to cutting thin strips of any material on any make of saw.

As far as using full size saws, running blades backwards or using a chop saw, if you value your model or your personal safety, they have no place in our workflow. If you are really determined to test these ideas, stick the part on the end of a broom handle before you attempt the cut. A Dremel Saw will cut your finger off. A full size saw can kill you.

And as a final note from Norm Abram: “Before we get started I'd like to take a moment to talk about shop safety. Be sure to read, understand and follow all the safety rules that come with your power tools. Knowing how to use your power tools PROPERLY will greatly reduce the risk of personal injury. And remember this. There is no other more important safety rule than to wear these, your safety glasses.”

Randy Danniel


Dennis Storzek
 

I agree with much of what Randy said. The biggest advantage of a saw with a sliding table (or a "sled" custom built to rid in the miter gauge grooves in a standard table) is you don't have to slide the part on the table; you can build whatever fixturing is needed to hold the part in a fixed, repeatable position, so it can't flex, or creep into the blade from the side.

A word about blade geometry... there have been a lot of terms bandied about, let's define them.

SET is the widening of the blade at the tips of the teeth, the purpose which is to reduce the friction of the work against the body of the blade. The traditional way to do this, still used on cheap carbon steel blades, was to bend (set) alternate teeth alternate directions from the blade centerline. This leaves the tips of the teeth as sharp outward facing points, and if the work moves AT ALL, they will score the work in the sides of the cut. I'm sure everyone has seen boards with "saw swirls" along the edge.

To prevent this, HOLLOW GROUND blades were developed. These expensive specialty blades have the entire plate of the blade ground thinner from both sides, so the rim where the teeth are formed is thicker. The teeth have almost flat sides (maybe one or two degrees of taper) so the tips of the teeth can't score the work, but they create more friction in the cut.

Carbide tipped blades handle this a bit differently, by making the separate brazed on carbide tips wider than the plate of the blade, but there are still differences. Some blades have relatively big carbides ground parallel (some people think the carbides are so big so they can be resharpened many times, but they are that way to provide bearing on the sides of the cut so the teeth can't score). Cheap carbide blades have tiny little tips, often ground at an angle that mimics the set of a carbon steel blade, for a maximum reduction of friction. These can score the sides of the work.

TOOTH GRIND is a separate issue. Blades meant for cutting wood across the grain are ground at an angle, alternately right and left, so the little points are most effective for severing the fibers of the grain. The carbide equivalent is called ATB (Alternate Top Bevel). Blades made for "ripping" wood (cutting with the direction of the grain) are ground straight across, because the chisel shape is most effective at excavating material from the cut. Metal working blades (alternately called "slitting saws" in the jeweler's trade, and "slotting saws" by machinists) are ground straight across, because metal has no fibers to sever.

TCG (Triple Chip Grind) is a variety grind of carbide tipped teeth that has a different grind on successive teeth, the idea being to break the material to be removed into smaller pieces. One tooth cuts a flat bottom V, taking a bite out of the middle of the kerf, the next tooth has sharp corners and cleans two smaller chips out of the corners of the V. They work well in laminate faced particle board, being less likely to chip the laminate, and well enough in other kinds of wood that they tend to be sold as "all purpose" blades. They work better in plastics than ATB or conventional crosscut blades, but not quite as well as the straight across grind, but are a lot more common.

What does it all mean? Well, Randy's suggested slitting saws will give a smoother cut in plastic than the common stamped carbon steel blades typically supplied with cheap hobby saws, and TCG carbide blades will do almost as well, at the expense of risking melting the sides of the cut from excessive frictional heat. The way to deal with the heat is to run the blade slower, or use a sliding table or "sled" to better fixture the work so it can't creep into the side of the blade, or ideally, both. A spray bottle of water for use as a coolant and cutting fluid will help also. With good fixturing the bade does not need to cut both sides and roof of the model at once, because positioning is repeatable and the body can be separated with three separate cuts, allowing the use of smaller blades and less blade projection.

Dennis Storzek


spsalso
 

My advocacy for a large diameter saw blade is so that the operation can be done with a single cut.  If there is a fixture that can hold a car accurately for three successive cuts, I agree that it might well be preferable.  I think showing such a fixture here would be extremely useful for those who are planning on using a small-blade saw, since the saw AND the fixture are both necessary elements.


Ed

Edward Sutorik


spsalso
 

There is another way to a square "cut" on a car body:  use a milling machine.

Not only is it extremely unlikely that you will damage the part (if you're the least bit competent); but there is almost no physical danger, as your pinkies are busy twisting dials at a goodly distance from the cutter.  And it is VERY accurate.



Ed

Edward Sutorik


qmp211
 

Not only will you spend more time making the jig/fixture than makin' the cut, IMO you will never get the car sides clamped tight enough to prevent a blowout using a mill. Again, cutter speed and feed rate are not conducive to acceptable results.

Sounds like I'm being argumentative. I'm not. Hundreds of hours of thought, design, engineering and destructive testing - most unintentional - have made me very skeptical. Our goal has always been repeatable results.

Even our 6" radial arm saw has problems with boxcar sides using fixtures cast to fit the shell. Plumb and square are enormous issues to resolve by cutting.

Buy 2 cars, cut long and sand. You will never be disappointed unless you didn't cut long enough....

Randy Danniel


qmp211
 

I agree to the concept of one cut. The problem is locating the part in 3D geometry relative to the blade to make the cut.

Randy Danniel


spsalso
 

Randy,

I am a machinist.  I spent at least 40 hours over the last two months machining styrene.  In this case, exclusively with a mill.  I assure you, professionally, that cutter speed and feed rate were not a problem.  I clamped everything appropriately, and there were no "blowouts".  Only thing wrong was the white fuzz all over the place.  The static-y white fuzz.

You are right about setup frequently taking longer than the work.  I have made many fixtures.  It may well take longer using a mill than a table saw; but much less can go wrong.

I bought 2 cars, cut long and sanded.  More than once.  I'd prefer not to do it anymore.  I do not enjoy it.


Ed

Edward Sutorik


Dennis Storzek
 




---In STMFC@..., <milepost206@...> wrote :

I agree to the concept of one cut. The problem is locating the part in 3D geometry relative to the blade to make the cut.

Randy Danniel
=======================

Well, as long as you are using a blade with no set, or big carbide tips with parallel sides, you can use the technique I used to use for splitting wooded card boxes, etc, in a previous career: Shut the blade down, flip the box / boxcar, fit the blade into the end of the kerf just cut, start the saw, and cut the next side. This doesn't work well if your saw has bad bearings or the blade wobbles as it comes up to speed.

You have to plan your cuts so there is always a kerf on the leading edge of the work.

Dennis Storzek