# Part for Ken



## Janger (Aug 15, 2021)

my buddy Ken who is a woodworking expert needed a block for measuring saw blade offsets for dovetail making. He had a design which I executed today. I got it to within a thou or so on each side of the block. The idea is the step down is 0.023 on one side 0.024” on the next etc. The results are ok but i would have been happier with 2 tenths accuracy not a thou.

I milled it vertical in the vise with a 3/4EM milling off the sides to depth. Question if I instead laid the part sideways and face milled the depth would it be more accurate? How could I mill this more accurately?


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## Janger (Aug 15, 2021)

Part in progress. Here i was milling the sides with the 3/4 EM.


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## PeterT (Aug 15, 2021)

Can you elaborate on the datum direction you are measuring against?


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## RobinHood (Aug 15, 2021)

Janger said:


> Question if I instead laid the part sideways and face milled the depth would it be more accurate? How could I mill this more accurately?








Yes, that should be a better approach. Step one is to deck off the surface A with a cutter (face mill or end mill). That is your reference 0. Now either move the quill down by 0.023” or the knee up 0.023” (whichever you know gives the greater accuracy) and machine the step. You eliminate tool deflection for the most part doing it that way. Flip the part 90* in the vise and deck off surface B to create its ref 0 and then machine the step.

If I understand the part correctly, the only critical dimension is the size of the step and that the two created planes be parallel to each other.

Side milling causes larger tool deflection than face milling and thus make dimension control much harder. The surfaces may also not be parallel because of the tool deflection.

The only way to do better than your HAAS, is to machine oversized by a couple of thou and then surface grind the flats.


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## DPittman (Aug 15, 2021)

Someone needs 2 tenths of a thou accuracy in their wood working tools and I'm still aiming to get .001" consistency in my metal work.  Ha ha.  Nice work man.


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## Janger (Aug 15, 2021)

Rudy's got it. That is the approach I was thinking would be better. More accurate at a cost of 6 setups instead of 2. The way I was doing it I can reach 5 sides at once and then flip it over to mill off the excess. 

>>The surfaces may also not be parallel because of the tool deflection.
Yes that also appears to be an issue, the part thickness varies over the face. Less than a thou but it's measurable. 

Thanks for the feedback.


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## RobinHood (Aug 15, 2021)

Any time John.


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## PeterT (Aug 15, 2021)

I see it now. Yup exactly as RH suggests. You are easily in DOC range of a 3-5 insert face mill, take it off in one pass with mirror finish. Only downside is repeat Z position zero & then Z position target for each face, but this is probably the best accuracy. You probably chance deviation by re-clamping if you tried to flatten the faces of a batch in one run & make the target DOC in another run.


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## kevin.decelles (Aug 16, 2021)

you need to get the 4th/5th axis going!  eliminate the additional setups!


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