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Forum topic by MrRon posted 11-05-2017 07:08 PM 592 views 0 times favorited 14 replies Add to Favorites Watch
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MrRon

4496 posts in 3082 days


11-05-2017 07:08 PM

Topic tags/keywords: miter saw radial arm saw

Before sliding compound miter saws(SCMS), there were radial arm saws(RAS). Miter saws then added rails so the head could slide rather than to just cut on the “chop” stroke. It now resembles the RAS, except for the “chop” feature. Why is it said to pull the head forward, then put in the chop position and then push the blade away from you. This doesn’t make sense to me. Pushing the blade away from you with the teeth cutting on the up stroke would, I observe, tend to lift the wood up away from the table as shown in the top sketch. In the bottom sketch, the cutting action tends to press the wood down against the table. The Ras also tends to self feed, but that is minimized by using a blade with positive rake.


14 replies so far

View Carloz's profile

Carloz

981 posts in 430 days


#1 posted 11-05-2017 08:13 PM

Cutting tools like saws and routers behave very unpredictably when cutting along the blade rotation.

View MrUnix's profile

MrUnix

6012 posts in 2038 days


#2 posted 11-05-2017 09:28 PM

RAS has a fixed arm that won’t allow the motor/blade to kick up… SCMS will. If you have ever pulled back on a SCMS and had it hit the wood, you will know why. Cutting from front to back (SCSM) causes the direction of cut to push the blade down towards the table. There is nothing unpredictable about it, just physics.

Cheers,
Brad

-- Brad in FL - In Dog I trust... everything else is questionable

View timmib's profile

timmib

10 posts in 604 days


#3 posted 11-05-2017 09:46 PM

I’m not sure what your question is. The design of a RAS is such that if you are ripping the cutting head will/can race towards the operator.

-- Kim, Chillicothe, MO

View jbay's profile

jbay

1857 posts in 738 days


#4 posted 11-05-2017 11:59 PM

”Why is it said to pull the head forward, then put in the chop position and then push the blade away from you. This doesn’t make sense to me.”

I’ve never heard that that is what is said. Personal preference as far as I know. (which may not be much)

I don’t like chopping into the wood and pulling because of the stress it puts on the saw with so many teeth cutting into the board at one time. (see below)

I’ve never experienced the wood lifting from the table so in my experience that’s a non factor for me.

Chopping into the wood compared to pushing into the wood:

-- If anyone would like to see my Portfolio, PM me and I would be glad to send you the link.

View Rick_M's profile

Rick_M

10640 posts in 2219 days


#5 posted 11-06-2017 02:54 AM

The Ras also tends to self feed, but that is minimized by using a blade with positive rake.
- MrRon

I think you meant to type, negative rake.

The answer to your question is to avoid climb cutting. Same reason you feed against the rotation of a router bit.

-- http://thewoodknack.blogspot.com/

View Fred Hargis's profile

Fred Hargis

4762 posts in 2332 days


#6 posted 11-06-2017 11:40 AM



I m not sure what your question is. The design of a RAS is such that if you are ripping the cutting head will/can race towards the operator.

- timmib


Actually if you are ripping (something I don’t do on mine) the cutting head should be locked and turned 90°, there’s no way it can “race” at you. But the work piece can sure come flying out…among other undesirable happenings. But even on a cross cut, the head can’t “run at you”. Because it’s held firmly by the arm, what happens if the self feed is bad enough is the blade gets jammed and stalls the motor.

-- Our village hasn't lost it's idiot, he was elected to congress.

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jonah

1471 posts in 3137 days


#7 posted 11-06-2017 03:10 PM

The rotation of the blade when you’re pushing towards the fence wants to fling the work piece forward away from the blade and down away from the blade. In both directions there’s a metal table preventing that from happening.

It’s the same with a table saw, just on the other side of the blade. The blade wants to fling the piece towards you and up.

View Carloz's profile

Carloz

981 posts in 430 days


#8 posted 11-06-2017 03:54 PM

.

View MrRon's profile

MrRon

4496 posts in 3082 days


#9 posted 11-06-2017 05:41 PM



The Ras also tends to self feed, but that is minimized by using a blade with positive rake.
- MrRon

I think you meant to type, negative rake.

The answer to your question is to avoid climb cutting. Same reason you feed against the rotation of a router bit.

- Rick_M


Yes! I did mean negative rake; thank you for the correction.

View Srini's profile

Srini

29 posts in 619 days


#10 posted 11-06-2017 09:53 PM



RAS has a fixed arm that won t allow the motor/blade to kick up… SCMS will. If you have ever pulled back on a SCMS and had it hit the wood, you will know why. Cutting from front to back (SCSM) causes the direction of cut to push the blade down towards the table. There is nothing unpredictable about it, just physics.

Cheers,
Brad

- MrUnix

How does Cutting from front to back (SCSM) causes the direction of cut to push the blade down towards the table? As Mr.Ron shown in the diagram, when you cut from front to back (away from operator), the blade cuts fresh stock in its upwards direction (that is what the leading edge of the blade in that direction).

I think Ron’s question is not answered.

View MrUnix's profile

MrUnix

6012 posts in 2038 days


#11 posted 11-06-2017 10:24 PM

How does Cutting from front to back (SCSM) causes the direction of cut to push the blade down towards the table? As Mr.Ron shown in the diagram, when you cut from front to back (away from operator), the blade cuts fresh stock in its upwards direction (that is what the leading edge of the blade in that direction).
- Srini

The resistive force applied to a cutting edge is opposite its direction of travel. If the blade is cutting from the top, it wants to push the blade upwards. If the blade is cutting from the bottom, it wants to push the blade downwards. Same deal with a router, which many people are more familiar with (but left/right instead of top/bottom).

Cheers,
Brad

-- Brad in FL - In Dog I trust... everything else is questionable

View Rick_M's profile

Rick_M

10640 posts in 2219 days


#12 posted 11-06-2017 11:12 PM


I think Ron s question is not answered.
- Srini

I answered it.

-- http://thewoodknack.blogspot.com/

View sawdustdad's profile

sawdustdad

335 posts in 724 days


#13 posted 11-07-2017 01:59 AM

Funny. I just took my 35 year old Craftsman RAS to the dump last week. Haven’t used it in at least 15 years. Set it down in the “free stuff” pile at the county’s waste transfer station. Been using a SCMS for all cross cutting.

-- Murphy's Carpentry Corollary #3: Half of all boards cut to a specific length will be too short.

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MrUnix

6012 posts in 2038 days


#14 posted 11-07-2017 02:03 AM

Funny. I just took my 35 year old Craftsman RAS to the dump last week. Haven t used it in at least 15 years. Set it down in the “free stuff” pile at the county s waste transfer station. Been using a SCMS for all cross cutting.
- sawdustdad

Depending on which model you had, you might of got $100 for it through the recall. I picked up one for $65, sent in the motor for $100, and am turning the frame into an overarm router table :)

Cheers,
Brad

-- Brad in FL - In Dog I trust... everything else is questionable

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