There can be a number of reasons that one gets bad threads. Some things to check are as follows:
The easiest and most often overlooked piece of the puzzle is the oil. Just like in a car it can break down and not perform as it needs to leading to poor threads and lower than expected die life. A quick check can be done by simply checking to see the amount of residue in the oil reservoir. Once the machine is off, unplug it and remove the chip tray. Then you can take a putty knife or even a screwdriver and scrape the bottom of the reservoir, if you bring back a collection of sludge on the tip of the too used then it is time to change the oil. That sludge will need to be removed and the reservoir flushed out with mineral spirits prior to refilling the machine with oil.
Another thing to check is the condition of the die head itself. Start with the die head post, this is the pin that plugs into the carriage when the die head is inserted to the machine. It should be perpendicular to the machine and secure. If it is bent or loose it can allow the die head to move excessively and create bad threads.
Another part of the die head is the cam plate, this controls the location of the dies and could also be the culprit. If the cam plate is worn on the die head it can allow the dies to move excessively and create a poor thread.
The condition of the carriage on the machine and the bearings of the machine itself can also be contributing factors. Both, when worn can lead to excess slop in the machine which can also lead to poor thread quality.
As you can see there can be many things that can go wrong and in some case it could be the material itself. It might be a good idea to give us a call and we can help you diagnose these things in more detail. It may save you a trip to a service center.
I hope this is helpful.
If you still have questions or concerns please contact Technical Support at 888-743-4333.