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 Bosch Colts are created equal. The
best test we have been able to come up with to see if a Bosch Colt (or Rigid 2400) will work with
our collets is:
- take a BOPG-COLT-1/8 (or BOSG-COLT-1/8) collet, a 1/8" calibration blank, a few Q-tips and a fine-tip permanent marker to the store with you
- remove the OEM nut/collet from a store model (probably good idea to ask the store clerk for permission first)
- clean out the router's tapered bore with a Q-tip
- use the permanent marker to draw 2 broad, heavy lines, 180° apart, from the inside of the tapered bore to the mouth (widest part)
- let the ink dry (we do NOT want to smear it during this test, we want sharp, easily seen scratches)
- insert the calbration blank all the way into the collet with about 1/8" hanging out the back
- using your thumb and index finger, press the collet FIRLMY into the bore
- grip the end of the calibration blank with your other hand and see if you can wigggle the collet back and forth
- leaving the blank in place and holding the router shaft to keep it from turning, rotate the collet in the bore 2 full turns with moderate pressure
If the collet seats snugly (no perceptible movement), it is probably a good match. If there is any apparent movement between the collet and the router shaft, remove the collet and look at the 2 black lines that you drew inside the bore
- If the ink is only rubbed away deep in the bore, about where the end of the collet would hit, the collet is bottoming out against the narrow part of the taper. This indicates that the bore taper-angle is larger than the collet taper and, unfortunately, incompatible with our collets.
- If the ink is rubbed away near the mouth of the taper, or evenly along the length of the line, the collet taper and the bore taper have a relatively good match. The collet will probably work quite well with this router, in spite of the slight movement you might have felt above.
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
Update March 1, 2011 - With over 1,000 kits now sold, we have been notified of 10 cases where our collets simply would not work, and in many cases, were worse than the OEM collets. I suspect that there are more such cases that have not been reported since our 1/8" collet offers the best solution to the absence of one from the manufacturer.
Update May 10, 2012 - By the middle fo June, 2011, approximately 20% of all Bosch Colt kits (BOPG-COLT, BOHG-COLT & BOSG-COLT) sold were being reported as incompatible with the lower priced Colt routers that appeared at the beginning of 2011. By the end of July, the numbers of failures had started to decline. By September, failure rates had dropped to pre-2011 levels and have held steady since then at around 1%. However, this apparent decline may be the result of more users pre-screening Colt and Rigid routers in big-box stores before purchasing them.
Update October 1, 2012 - Recent reports from customers and forum posts indicate that the proportion of compatible Colt routers has fallen to below 50%. Before you commit to a purchase, take time to test the router as detailed above to make sure it will work in your application.
Update May 15, 2013 - New Bosch-Colt compatibility with our collets is now running between 20 and 30%. This is based on converesations with customers who have literally tested every Colt in their local big-box store and reported the results to us. We are advising manufacturers of compact CNCs to consider switching to the Dewalt DNP611 as their default spindle offering.
Update October 15, 2013 - Bosch-Colt compatibility is now running less than 50%. Buyer beware.
Update October 15, 2013 - We are starting to get reports that similar problems are cropping up in the Porter-Cable 890 family. So far there have only been 5 reports in the past 5 months, but it is cause for concern. The Bosch 1618 EVS or Hitachi M12 might be better choices if your are looking for a good, mid-sized router.
Update January 1, 2015 - We have dropped the Bosch Colt, Rigid R2400 and Porter-Cable 890 family from our list of supported routers.
The Bosch 1617/1618 and Hitachi M12 routers are the same diameter as the Porter-Cable 890 series (3.5 in.) and are drop-in replacements.
The Dewalt DWP611 is 2mm (0.080 in) smaller in diamter than the Bosch-Colt and Rigid 2400 but is compatible with most mounts with the use of shims.