Checking RPM

[JPG]

Today I received a package]Hmmmm...Could it be that the tach is wrong? Will the speed change when I attach a saw blade and arbor?
[/SIZE]

Close to what I observed(twas a surprise also!). Mountainbreeze posted similar readings.

If you have an opportunity to check the motorspeed(fan/floating sheave), it should be close to 3450(?). [or whatever the nameplate says - may be higher 'noload']

I do not think a blade/arbor by itself will change it much(if at all).

A reading over 3600 would absolutely indicate the tach is reading high.

[billmayo]

My headstock runs faster than expected at both ends.

LOW = 1000 rpm (SB 700) while the HIGH = 6650 rpm (SB 5200)

Hmmmm...Could it be that the tach is wrong? Will the speed change when I attach a saw blade and arbor?

I would believe most of the headstock quill speeds are reading correctly with the tachs. However to check the tach, put a piece of reflecting tape on the outter side rim of the Floating Sheave and see if the tach shows 3450 RPM. These are the range of speeds I see on customers headstocks before replacing the motor belt and doing the high speed adjustment. The maximum speed will increase as the motor belt wears.

Shopsmith recommends the motor belt be 1/8" - 1/16" away from the outter edge of the motor pulley. I would believe your motor belt may be even or sticking up to 1/4" above the edge of the motor pulley for the faster speeds. Adding a saw blade and arbor should have minimum effect at any speed.

[dusty]

I received my $2.47 tachometer today and it seems to be working FINE.

I am not, however, feeling that good about headstock speeds in general. My speed tests all indicate that the headstock is operating at speeds above what are expected.

The motor itself is close. It reads 3570 which is about 3% over the anticipated speed. Based on this, I consider the tachometer to be reasonably accurate.

I'll report in greater detail (if I discover anything) as I go but in general my headstock speeds, measured at the upper spindle) are higher than that.

At A on the speed dial (750rpm) I measure 1045rpm. At FAST on the Speed Dial (5200rpm) I measure 6650rpm. My headstock is running about 30% higher than normal. This deviation is near the same for ever position on the speed dial.

Now that I see the rpm numbers, the headstock sounds like it is "screaming" at top speeds. It was not all that bad before I got a hold of the tach.

[JPG]

I received my $2.47 tachometer today and it seems to be working FINE.

I am not, however, feeling that good about headstock speeds in general. My speed tests all indicate that the headstock is operating at speeds above what are expected.

The motor itself is close. It reads 3570 which is about 3% over the anticipated speed. Based on this, I consider the tachometer to be reasonably accurate.

I'll report in greater detail (if I discover anything) as I go but in general my headstock speeds, measured at the upper spindle) are higher than that.

At A on the speed dial (750rpm) I measure 1045rpm. At FAST on the Speed Dial (5200rpm) I measure 6650rpm. My headstock is running about 30% higher than normal. This deviation is near the same for ever position on the speed dial.

Now that I see the rpm numbers, the headstock sounds like it is "screaming" at top speeds. It was not all that bad before I got a hold of the tach.

I have found that it produces readings that are closer to 'expected' if the reflective surface is a small percentage of the total area being 'observed'. i.e. a thin strip on a pulley of significant diameter(1/2", 5"). It doesn't seem to work well on smaller diameter 'targets'. So I think a 6" faceplate
is a better check than a shaft itself.
Got my power station reassembled(motor) and greatly increased the belt tension(too much). The speed range measured about 900 to 3900. I expect that to drop with decreased belt tension. The belt flopping diminished greatly though! Goldie will be next. I think it is running 'fast also'.

[dusty]

I have found that it produces readings that are closer to 'expected' if the reflective surface is a small percentage of the total area being 'observed'. i.e. a thin strip on a pulley of significant diameter(1/2", 5"). It doesn't seem to work well on smaller diameter 'targets'. So I think a 6" faceplate
is a better check than a shaft itself.
Got my power station reassembled(motor) and greatly increased the belt tension(too much). The speed range measured about 900 to 3900. I expect that to drop with decreased belt tension. The belt flopping diminished greatly though! Goldie will be next. I think it is running 'fast also'.

My Power Station appears to be "right on". Measured speeds range from 881rpm to 3856rpm so I'll not mess with it right now. This also seems to indicate that the tach is reliable.

I am not measuring right on the shaft but I will do some experimenting with places to mount the reflective tape. When the reflective tape is improperly positioned or sized, I believe it will produce inconsistent readings rather than inaccurate readings.

[JPG]

My Power Station appears to be "right on". Measured speeds range from 881rpm to 3856rpm so I'll not mess with it right now. This also seems to indicate that the tach is reliable.

I am not measuring right on the shaft but I will do some experimenting with places to mount the reflective tape. When the reflective tape is improperly positioned or sized, I believe it will produce inconsistent readings rather than inaccurate readings.

I haven't tried the reflective tape yet. I be using plain old creme colored masking tape. I figure I will always have some of that. Not so the reflective tape!

[JPG]

Finished up fiddling with the power station. Position of motor mounting bracket is 2" below the 'top'. The measured speeds(top/bottom) were 3900 and 943 with the motor measuring 3560 and 3570 respectively. At that tension, the control lever can be moved smoothly from low to high. When not tightened down, the lever drifts to slow(1) and stabilizes there. The lever force increases slightly when moving from 8 to 9.

If the belt were tighter, moving the lever to higher speeds requires considerably more force.

IMHO with the belts I have, the best position would be slightly less than 2".

It is interesting to note that the belt between the variator and the output shaft pulley is quite slack in high speed. The belt tensions are more equal at low speed.

The motor speed was about 3% high which is not unusual for no-load condition. Notice it slowed slightly when adjusted to high speed.

Adjusting the measured speeds for the faster motor speed yields the 3450 motor speed correction to be 911 and 3774 rpm.

A side tidbit, the variator rpm is 1640 and 3335 at low and high speed respectively.

[dusty]

I used my new tachometer to reset the high speed adjust setscrew. With the top spindle rotating at 5200rpm, the setscrew was adjusted just as instructed in Nick's Sawdust Session.

It is probably psychological but I think the headstock sounds a lot better now. Prior to doing this setting, the top spindle was rotating at 6650rpm when set to FAST. It is now at 5248 +- a little.

[beeg]

Is there a chart by SS around that shows the RPM's for each letter?

[mountainbreeze]

According to the Owner's Manual that came with my Mark V...

A - 700
B - 800
C - 900
D - 1000
E - 1100
F - 1200
G - 1400
H - 1600
I - 1800
J - 2000
K - 2200
L - 2400
M - 2600
N - 2800
O - 3000
P - 3200
Q - 3400
R - 3600
S - 3800
T - 4000
U - 4200
V - 4400
W - 4600
X - 4800
Y - 5000
Z - 5200

Mine is a bit faster than this table indicates it should be. I'm +300 at "A" and +1340 at "W". Also, even though it's in the book, I don't have an X, Y, or Z on my speed dial.