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Many solid tube mass produced scopes can see the primary mirror set too close to the focuser. Many reasons for this. One is the OTA set up as a dob is the same one that is used for astrophotography, and this requires the primary mirror to be placed closer to the focuser/secondary for the camera to achieve focus - to make a whole new tube line just for visual use is commercially unviable. Another thing is the true focal length of any mirror expressed in the focal ratio is not exactly true to the millimetre. There will be variations between each, and sometimes significant differences longer or shorter.
If the draw tube does not ruck out sufficiently to achieve focus, you can pull the eyepiece out of the draw tube, even upto half way out. Another option is to get an extension tube. My 8" dob is specifically made for photo, so the primary mirror is closer to the focuser, and I have no way of achieving focus for visual if I don't use an extension tube.
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