Steps being left in cut

[kmacht]

I need some help. I build a slightly enlarged JGRO type router. The machine works excellent except for one problem. If I try to cut something like a 3x3 square out of 3/4" mdf I keep getting left a stepped line one one side of the square. There is a step at each depth of pass. Each step extends out a little further than the last one. The other three sides are perfectly smooth. I initially thought it was maybe a backlash problem. I am using dumpster anti-backlash nuts on 1/2-10 acme rod. I checked backlash by putting a dial indicator on each axis, jogging it back and forth 1" and seeing if it went back to zero. It goes there every time. I also tried just jogging it .001 each way and it shows up as .001 on the indicator. My next thought was that maybe my spindle was out of square. I took a machinist square and held it up next to my bit and I can not see any gaps anywhere around the bit. I also thought maybe I was missing steps but I am running at a fairly slow feed rate (30ipm) and a very conservative depth of cut (.100) for mdf. That and the steps are repeatable if I cut out multiple parts. I am stumped at this point. Any suggestions?

Keith

[DonFrambach]

It sounds like one of your couplers is not sufficiently tightened. It is progressively slipping hence the stepped cuts on one side.

[lunchtrayrider]

are you sure the bit is straight?

[beermkr]

I expect you may find that the bit is tilted one direction. Slanted with the top towards the part on the side that is stepped. The opposite side gets cut off each time.

R/

[kmacht]

Any good way to check to see if it is straight or is it just trial and error?