First op depth is off

[Djstorm100]

I've been trying to not rush my own parts and take time to analyze ever step/op. I notice my part (which is suppose to be 0.5" thick is actually .478. I'm going by memory but will be going by the shop at the end of the day to confirm. I am using the end of the caliper to measure. It's not really made to do this but it works-ish.

Setup:
I'm using parallels. This is for first op.
Back left corner for Y,X. Top for Z

What I've done:

Machine is barely 4 months old and I do not run it hard.

Confirm tool offset by using a Mitutoyo Zero Setter
Check Hiamer height
Tram of vise

Check axis movement.
I'll use a indicator and zero the axis rapid out 8" and rapid back in. It's with in 0.0005.

What I plan to do this evening
Use 0.0001 steps to see how much lost motion I have

Cam levels zero axial and 0.005 radial. Using a 3/8 zrn cutter at 3,600 RPM at 0.002 chip load

Material:
6061

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[joshetect]

put an indicator on the work when you are closing the vise jaws. I find that if using my soft jaws, the movable jaw has a bit of lift if I am trying to hold onto say 1/4" of material.

[Djstorm100]

put an indicator on the work when you are closing the vise jaws. I find that if using my soft jaws, the movable jaw has a bit of lift if I am trying to hold onto say 1/4" of material.

Sorry I should of stated I'm using parallels. This is for first op.

[joshetect]

When clamping down the work, check your parallels. If the works isnt being pushed down, and its being lifted up you will be able to move them up and down a little. You can tap it down with a mallet, but sometimes that doesnt help.

I usually get my Z0 height off the parallels, if going off stock top thickness can vary. When checking the height, both top and bottom should be machined surfaces. I generally make my references a repeatable accurate surface, I rarely use the stock as the reference points.

[shred]

Also have you measured your stock? It's frequently not spot on-size and if it's running a bit undersize, that can be magnified in the part if you zero top of stock.

[Djstorm100]

I had gotten my numbers mixed up thinking the depth was off by .030 but at the shop last night measured the part and it's 0.005-5.5 off. Would like to get this number lower obviously but not sure how. Work offsets were confirm to be spot on. most were with in +/- 0.0001

I normally don't measure my stock but I have since a phone call with a friend. My stock is suppose to be 1.75 but it's 1.76/765. with it running over sizer I though it would still see the correct thickness. Now the stock I'm using is way over kill but it's free and works.

[syscore]

Generally, with raw stock, I face the top and bottom, and the resultant width is very close (< .001). If you want to do only one face op, then (as someone suggested) touch off from the parallel rather than the stock. You can use a 123 block on top of the parallel to do this (and offset by 1" of course). But if you are going to face both sides anyways, as part of the whole program, then touching off on the stock works fine.

[Djstorm100]

Generally, with raw stock, I face the top and bottom, and the resultant width is very close (< .001). If you want to do only one face op, then (as someone suggested) touch off from the parallel rather than the stock. You can use a 123 block on top of the parallel to do this (and offset by 1" of course). But if you are going to face both sides anyways, as part of the whole program, then touching off on the stock works fine.

With this the stock is deck and object is made. In op2 the once bottom (now top) is just decked.

[syscore]

With this the stock is deck and object is made. In op2 the once bottom (now top) is just decked.

I misspoke earlier. In order to get accurate height results, I use the parallels as the reference. My stock can also vary by 0.05" in thickness, and I just take that into account in Fusion and if the stock is 1" thick, I tell Fusion that it is 1.05" thick. The bottom back corner is used as a reference. The first pass might be light, but in the end, the height will be accurate. For stuff where height isn't critical, touching off from the top and measuring works fine.

[Steve Seebold]

Do you knock your parts down on the parallels before you start your cut?

Are you sure it’s not the vise that’s lifting the part off the parallels?

Are you programming from the top of the part down or from the bottom up?

[Djstorm100]

Yes I give them a good wack with a dead blow. The first op is off the top left corner.

So I ran the part again and optimized the cam a little...it's with in a 0.001 of 5" thickness. I hate not knowing what happen.