ADOC and RDOC relationship
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  1. #1
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    Default ADOC and RDOC relationship

    Can anyone that has experience with with High efficiency milling explain the relationship with ADOC and RDOC?

    Iíve recently been doing a lot of pocketing/profiling on a 3axis using a 20mm indexable tip cutter and have been playing around with the axial and radial cut depths to use more of a cutting edge to get better mileage from each tip. Iíve gone one step further and found a chip thinning adjustment formula which has really ramped up the total MRR.

    So far my logic is that if a cutter takes 5mm radially and 1mm axially that makes a cut area of 5mm^2. If I swap them and take a 5mm depth of cut and 1mm radially thatís the same cut area.

    So my question is can I think of this strategy as a cut area? Or because Iím using different areas of cutter geometry does this have a big affect on cutting forces? Can I increase my feed and speeds by a bigger factor or should I wind it back slightly by a certain percentage, depending on the ratio of ADOC and RDOC?

    If anyone has any other factors that Iíve not considered then please enlighten me, the goal is to as always balance a decent cutter life with a reasonable time. Itís mostly one off parts for extrusion tooling so time can be slightly sacrificed in favour for tool life.

    If it helps explain, Iím machining primarily 1.2316 which is a 13% chrome magnetic hot work stainless toolsteel used in it is delivered condition. (No heat treat stages)

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    Download this, it's my bible that I've been using for the last few years.
    Advanced CNC Speed And Feed Machinist Calculator - HSMAdvisor

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    This is just stuff off the cuff from what I've read or tried or general machining experience has taught me. I confess that I'm no expert on HSM.

    I think one of the guiding rules for HSM and where from what I've seen it gets promoted the most, is using the largest ADOC you can and adjust the RDOC to suit. Basically boils down to high feed at high DOC with smallish step-overs.

    Two factors come into play with high ADOC. One is your friend and the other not.

    Good - You're using the full length of the cutter which improves tool life and makes the most of what you got. Also many times you're finishing part features at full depth in one fell swoop. Well... multiple small fast fell swoops.

    Bad - High ADOC can start calling into play the rigidity of both the machine and the setup on it. And one might assume horsepower too. For the most part and combined with tool stick-out, these will be the limiting factors in your selection of RDOC. And depending on material being machined, possibly even more so then the amount of chip room in the cutter being used. I am uncertain how this balance plays out with high or very high flute count cutters used in some materials and generally asked for in HSM machining speak.

    Continued - High RDOC with low ADOC is less prone to this. Here tool stick-out could end up being your limiting factor. Any machine worth it's salt and using a short length tool could handle your example of 1mm DOC and 5mm step-over at practically any speed you throw at it. Though unless the part feature dictates it, I see no practicality to that set of parameters. Maybe this is the scenario that High Feed cutters want to play their game in. I have no experience with them.

    Also bad - Running a tool at shallow depths of cut is eventually going to water line it and make it unusable for other cuts with different depths. Also carbide tools in Stainless can be prone to notching at the cut depth line. (Stock surface.) Notching near the very top of the cutting zone/edge is going to be less of a problem when used elsewhere.

    Last word - try to use tools with some amount of edge rounding or chamfer. You'll get a lot more life out of them in HSM. Your insert tool likely has plenty.

    I looked at the HSMAdvisor listed above. Although the UI is very different, it appears to have all the same inputs and fields that G-Wizard Feeds & Speeds Calculator has. This is something I've used for years with success. Although I'm curious to try HSMAdvisor for fun and comparison. Both calculators seem reasonably priced.

    Dave

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    Thanks for the HSM advisor suggestion, will check that out and compare the figures Iím getting currently.

    Also, yer I agree with what you say, we seem to be on the same page, I use an indexable cutter for roughing and saving the end mills just for finishing, this seems to be our best value solution so far.

    Looking at the indexable cutting info on the box, it gives cutting speeds, chip per tooth and cutting edge length, this info is enough to get a speed and feed but not an area of cut or MRR, how else can I work out the max RDOC with out pushing it too far and breaking the cutter?

    Assuming that the work piece is nice and solid and weíre working within the machines power, (Iíve never seen it go above 20%)

    The tip makers donít give any other info apart from whatís on the pack.

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