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TIR Measurements on a Bosch Colt Palm Router (TIR
exceeds specifications) |
Without exception, the Bosch Colt Variable-Speed
Palm Router (PR20EVS) is, in our humble opinion, the best trim router on
the market. The bearings are exceptional, the motor noise relatively
low, and TIR (Total
Indicated Runout) low enough to consider this tool a
suitable spindle for light-duty CNC machining.
To be honest, the OEM nut and collets could use some work and the
absence of a
1/8" collet from the manufacturer has, until now, substantially
reduced its utility in digital woodworking and printed circuit
fabrication.
Unfortunately, as with any consumer grade appliance, manufacturing
tolerances can vary enough to make some members of this family of tools
unsuitable for precision work. Such is the case of the Colt graciously
sent to us by Chin-Kai Chang of iLabs at USC (University of Southern
California).
During his evaluation of our
BOPG-COLT nut and collet set, he found that no amount of cleaning, tightening,
or adjusting would bring the TIR into specification. His series of videos
(which can be
seen on
YouTube) clearly show that his evaluation technique was quite good and that
he was very capable of performing precision measurements.
When our testing lab received his Colt (complete
with both the OEM and BOPG-COLT nuts and collets) we wanted to see if we
could figure out just what was going on. The test procedure is
best revealed through the following series of videos.
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Bosch OEM nut and 1/4" collet in
the TIR Test Stand
First we wanted to see how the OEM nut and collet measured when mounted in our TIR
Calibration Test Stand. Since we wanted to determine the
type of runout, we took measurements using a 1/4"
shank tool with a measured TIR = 0.000050" with the test probe adjacent to the face of the collet
(picture at left) which yielded TIR = 0.0046"
We then moved the probe to a point 1.25" down the shank from the collet (picture at right)
showing a TIR = 0.0083".
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Bosch OEM nut
and 1/4" collet in the Bosch Colt Palm Router
Next we mounted the OEM nut and collet into the Bosch Colt and measured the TIR
at the face of the collet. (see picture at left). At TIR = 0.0023", it
was actually better than the results using our test stand.
I cannot find the video of the measurement at
1.25" from the collet face, but the test records indicate a TIR =
0.0056". Again, the results were better than on the test
stand. Since
I do not have a video of the test, here is a picture of my lab.
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BOPG-COLT nut
and 1/4" collet in the Bosch Colt Palm Router
Prior to sending us the Bosch Colt to test,
Chin-Kai had shown that
our BOPG-COLT collets,
when mounted in his router not only failed to meet our published specifications, but were substantially worse
than the OEM collet.
Naturally we had to see for ourselves. As above, the video on the left shows the results of
measuring the runout adjacent to the collet face (TIR=0.0051" ), and the video on the right with the probe about
1.25" down the shank (TIR=0.0131").
Zut Alors! Truly abysmal! |
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BOPG-COLT nut and 1/4" collet in
the TIR Test Stand
Our first thought was that, even though our BOPG collets are 100% inspected to insure
compliance with the published TIR specification of < 0.0004", the
collets shipped to *** were defective and should not have passed. When mounted in the test stand,
that did not prove to be the case. As above, the right picture is the TIR measured
1.25" down the shank
(TIR=0.0008").
Measurements at the face of the collet yielded TIR = 0.0003". |
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BOPG-COLT nut
and 1/8" collet in the Bosch Colt Palm Router
But what about using the 1/8" collet in the
Colt? As the video shows,
the results were not much better than the 1/4" collet. The TIR measured at the collet face
= 0.0043" (left) and about 1.00" down the shank the TIR = 0.0083". Ten
times greater than the specifications and totally unusable for working with tools less than 0.0938" dia.
Actually, runout that severe makes the collet useless for any kind of precision work. |
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BOPG-COLT nut
and 1/8" collet in the TIR Test Stand
Again the question arose. Was this collet simply a defective part that fell through a
crack in our inspection protocols, or was something else going on? Only one way to find out. We mounted it in the TIR Test Stand and
repeated our standard QC measurements.
At the collet face TIR = 0.0003" and 1.00" down the shank TIR = 0.0003".
Well within specifications.
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After a fair amount of discussion and measurements
inside the taper of the Bosch Colt, a rather disturbing fact emerged. The
angle of the taper was larger than that of any other Colt we had measured and
the wall did not form a linear cone. Rather, it bulged slightly inward in the center which prevented our hardened
(HRC 52 min.) spring collets from accurately seating in the spindle. Removing the nut from the collet we noticed that
when we pushed the collet into the taper it could be wiggled back and forth and could not find a secure seat
(a sure sign of a mismatch between the collet and taper geometries). It was not clear why the OEM collet worked
so much better than our BOPG collet. During discussions on this curious behaviour, it was suggested that, since the OEM collet
is not very well hardened, perhaps it was forced to comply with the deformation in the taper and was able to achieve a more
concentric seat. Unfortunately, we do not have the tools to accurately determine if this is true.
What does all this mean to the user? Not all Colts are created equal. The
best test we have been able to come up with to see if a COLT will work with
our collets is to take a 1/8" BOPG collet to the store with you and try it
in the taper bore of any Colt you are considering. If it seats snugly, it is probably a good match. If the
collet wiggles in the bore, it may not function at the
level of precision needed for fine detail work.
How common is this problem? Of all of the kits that
are now in the hands of end users, only two (2) Bosch Colts have proven to
be incompatible with our BOPG-COLT collets. Both of these routers were
purchased from the same source so they may have been part of the same batch.
As more test data comes we will continue to update our statistics. A good
place to look for ongoing reviews of our nuts and collets is
CNCZone.com. If you are
not already a member, you should be. It is one of the best sources of a wide
spectrum of wood/metal/composite machining on the web.
As with all of our tools, the collets, nuts, and spanners come with our
standard no-fault guarantee. If you cannot
find a COLT that will work with the collets, return the nuts and collets to
us for a refund. Cold comfort to be sure, but the best we can do at the
present time. |
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