Advantages with Adaptive / Dynamic Roughing for Rope and Knuckle threads.
Rope threads usually consists of large curved surfaces and therefore an equal depth of cut does not gives an optimal roughing process and can leave an uneven stock amount for finishing.
The Adaptive Roughing process works similar to Ridge Height in GibbsCAM mill contouring and will dynamically adapt each cut along a curved surface. The cut depth will continuously vary to maintain a uniform and parallel surface to the thread profile.
This type of roughing process can result in fewer cuts overall but most importantly, leaves a uniform stock amount for the finishing tool.
But let's first have a look at how a traditional roughing with equal depth of cut looks like on a large Rope thread.
Here we have a large Rope thread, and have divided the thread height into equal amount depth of cut (yellow lines). The circles are the only tooltip coordinates tangent to the stock amount. (pictured below)
This roughing process will leave an uneven stock thickness and this becomes more apparent around the root of the thread profile. There are a significant thickness difference.
The red area shows the varying stock thickness. This thickness difference can and most likely will impact the performance for the finishing tool in several ways.
Uneven insert wear for finishing tool as it gets increasing amount of material to remove.
Difference in spindle load for the finishing tool.
Difference in load and forces on the finishing tool and holder.
These differences can impact the surface finish and in worst case, introduce chatter around the root of the thread.
If these issues were instead happening in the roughing process, the finishing passes will get a smoother run, so lets compare with how the same scenario applies with Adaptive Roughing.
Adaptive Roughing in ThreadTracer.
Here we have the same large Rope thread as above. With Adaptive Roughing the depth of cut are adjusted smaller at the crest and root of the thread, and largest inbetween.
The circles are the only tooltip coordinates tangent to the stock amount. The yellow lines shows the distance between the different cut heights. (Pictured below)
Adaptive Roughing process makes a significant difference in stock thickness along the thread profile. Thickness around the root of the thread are the same as the rest.
This time the red area have an uniform stock thickness. This uniform thickness will give the finishing tool an equal insert wear along the thread profile and an even load for spindle and toolholder along the entire finishing process.
With Adaptive Roughing, the roughing tool will get less material to remove at the start, then the depth of cut will increase towards the middle, and decrease to smaller depth of cut at the root of the thread.
To get the same effect with traditional roughing, the only option are to set the depth of cut smaller than needed, significantly increasing the overall amount of cuts and time to machine the thread.
Adjustments for Adaptive Roughing
The adjustments for Adaptive Roughing are set with a dropdown menu. The set Stepdown Xr amount will be used as a base or reference value for the adaptive depth of cut calculations.
The radius of the thread profile compared to the selected tool radius will also influence the dynamic depth of cut values.
Under Adaptive Level there are 6 levels of adjustability (see red arrows).
These levels controls the aggressiveness for Adaptive Roughing, finer levels will calculate smaller cuts, and coarser levels will calculate larger cuts.
So for this Rope thread, we adjusted the aggressiveness to 3 different levels with the same base or reference Stepdown Xr
and got :
228 roughing passes, with a reference depth of cut of 0.5mm
317 roughing passes, with a reference depth of cut of 0.5mm
482 roughing passes, with a reference depth of cut of 0.5mm
With adjusting the base Stepdown Xr
to a suitable value for the material, the Adaptive Roughing will always give a good result.