Anomalous dimension. [FIXED]

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freman
Posts: 1594
Joined: Tue Nov 27, 2018 10:30 pm

Anomalous dimension. [FIXED]

Post by freman »

Hi,

I am having an oddity I can't understand.

I have bearing block based on the sketch below padded to 230mm.
In the sketch I can check the distance from bearing axis to the flat edge as 19.5mm ( shown ).

When I go to the path editor it seems the hole ( pocket ) is centred at 17.5mm from the edge which I have set as y=0 in the stock.
Using the cursor, both the horizontal and vertical centres of the pockets are 17.5mm from their respective, parallel surfaces.

I find it hard to imagine that this is being miscalculated, so it seems that I must be misreading something.

I'm not happy committing to metal before checking this is right since I don't have any spare blanks if I mess up.

Can anyone explain the apparent difference?

TIA.

PS. The sketch is a bit busy so to help visualise the part, it is a block with four bearings which run on a round 20mm bar. The rectangles are the side view of the bearings.



OS: Fedora 34 (Thirty Four) (LXQt//usr/share/xsessions/lxqt)
Word size of FreeCAD: 64-bit
Version: 0.20.24847 (Git)
Build type: Release
Branch: master
Hash: 20e756306d9aa624fcbf465f0345d721673ce720
Python version: 3.9.4
Qt version: 5.15.2
Coin version: 4.0.0a
OCC version: 7.5.0
Locale: English/United Kingdom (en_GB)
Attachments
pocket-sketch.png
pocket-sketch.png (66.5 KiB) Viewed 183 times
pocket-path.png
pocket-path.png (11.2 KiB) Viewed 183 times
anomaly.FCStd
(119.51 KiB) Downloaded 8 times
Last edited by freman on Thu Aug 26, 2021 8:14 pm, edited 1 time in total.
GeneFC
Posts: 2834
Joined: Sat Mar 19, 2016 3:36 pm
Location: Punta Gorda, FL

Re: Anomalous dimension.

Post by GeneFC »

Does not appear to be related to Path. The holes are at 17.5 mm in the original Body.

Here is your sketch with the holes shown. You can see that the centers do not line up with your expectations.

Capture.JPG
Capture.JPG (22.27 KiB) Viewed 132 times

Gene
User avatar
freman
Posts: 1594
Joined: Tue Nov 27, 2018 10:30 pm

Re: Anomalous dimension.

Post by freman »

Thanks Gene,

Yes, you are correct, it's not path in fact. I have tracked this down to sketch placement ( yet again ). The two sketches with the hole plans were not correctly positioned on the faces they were attached to. Earlier I was imagining it was all parametric and was confused why it did not line up.

At some stage I increased the bearing size and shim thickness, this shifted the block in the original sketch a little since it is all built off the round bar.
It seems that hole sketch placement did not follow. This maybe because I entered a manual offset of 4.5mm , or because the placement method did not follow the sketch changes.

It's a while since I did this model and I can't recall if I measured something off the main sketch I posted and manually entered it to place the other two. I have no clear recollection how I set the sketch placements.

I moved both the hole sketches and it all lines up now. Luckily I was attentive enough to spot this small error before the tool hit metal.

For once, FC cutting air saved me time :)

Thanks for your help.
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