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Discussion Starter #1
Step 1 manufacture RSP.


First job is get a good drawing. I'm using the left side plate as its nearly a mirror image. You need to measure everything three ways from Sunday AND then double check and then cross check it again. It takes way less time to prevent errors at this stage than to machine a part and find something out of spec. Or worse yet, rivet the weapon and find find something not quite right. (I've done that)

I measure it first with calipers and make a sketch. Then check the measurements with mikes. then check again with the DRO on the manual mill.

couple pics of this step
 

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Discussion Starter #2
Next draw it up in a CAD program. I use the free Draftsight X64. Did one layer for the outline, one for the relief or lightening cuts, one for the denial islands.
Then went back to step one and re double checked the drawing.
 

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Discussion Starter #3
The next step is decide how to machine the part.

I'll be holding a 14.85" by 4 by .25" stock in soft jaws on the cnc mill. Fist op will be just to spot drill and drill a few holes. Looks like only the return spring slot and a ruff hole at the back of the charge handle. I decided not to CNC all the rivet holes. Its actually better to just match drill these after clamping.

Next op will be the relief or lightening cuts with two tools, one to remove the bulk of the material and another to add the finish cut and all the radii. Plan "A" right now is a 1" Sandvik R390 to ruff out the bulk of the material. Then the final pass with a two flute HSS endmill custom radiused on my tool and cutter grinder.

Next step will be the outline of the weapon and charge handle slot. I'll be leaving several parts unfinished (see red lines on .pdf) so the part can stay clamped in the softjaws. These cuts will be done on the manual mill after the part is complete.

Then the part will be flipped over and denial islands cut. Right now, I'm thinking cut the backplate slot on the horizontal manual mill. This could easily be CNCed with a small endmill but a horizontal is light years faster. And I need something to do while watching the CNC do its thing. I'll also be doing the return spring slot with the manual mill.
 

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Discussion Starter #4
Next step is to write and debug the Gcode for the CNC mill. I don't own a decent CAM program, nor do I like them for the work I do. Been writing my own gcode for 25 years now.

There is a neat short cut for the gcode routes that I like. Just draw them up in the same CAD program the part was drawn in. This is mostly just copying a layer, deleting unneeded objects and then drawing connecting lines to make a route
 

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Discussion Starter #5
Then use a backplotter to convert the drawings to gcode. I use NCplot, got it for $60 back when it was developed. I've seen a free one for Mach 3 users.
 

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Discussion Starter #6
Next, write the actual gcode and test it on the CNC miil with NO tooling installed. My mill shows the route on the viewport. I included the actual Gcode for the outline cut and show a pic of the relief cut on the CNC's control screen.

i use something called parametric programming for the Gcode. That is the code has variables and loops (code repeated n times).



AT this point, I need to order the material and get and make the tooling, so it will be a while before any mores posts.
 

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Very interesting info - thanks. While I dabble at using a small RF30 Mill/Drill with good success, I am "cave-man era" next to your abilities. :drink:
 

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Wonderful thread Karl, nice to see how a professional tackles a job like this.
Please keep the pictures coming, maybe someday I'll own a kit and could use this information.
CaptMax
 

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Discussion Starter #9
THE POWER OF G41

Kind of an advanced topic, but I just figured it out and wrote the Gcode for this. G41/G42 is called cutter comp in Gcode parlance. It allows you to write the code for the actual outline and then tell the control what cutter it is using. That way you can change tooling (cutter diameter) and run the same Gcode to make the same part.

But you can lie to the control and really expand the use of cutter comp. If you tell the control the cutter is larger than it actually is, the control will offset the tool more and the part will be larger. One HUGE use of this is ruff your part out telling the control the cutter is a few thou bigger. Then for the finish pass, tell the control the right number. Now it will shave a few thou off for a perfect finish.

Here's an even more advanced trick. The relief, or lightening cut area, on the side of the RSP has a radius of 0.125". I want to make four passes each 20 thou deep for a total of 80 thou removed. The cutter route has to be farther away from the side each pass deeper. I've learned to always draw it out so a mistake isn't made. DRAW IT OUT should be the first commandment of machining.

I'm using a 0.5 inch radius or 1.0 diameter cutter for this. If the control is told these successively larger cuttter sizes, it will offset more and more to make the part just right.
 

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Looks good Karl. How come you are not copying the left side plate exactly with regards to the raised areas on the outside center of the plate?

Here is a picture of a original fn32 RSP for sale on gunbroker. I am not sure if it was a retracting handle or side trigger that mounted on the reinforced area.
pix859027070.jpg

Here is the back of mine, I am ready to rivet it together now.

 

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Discussion Starter #11
Not sure if there's an agreement on nomenclature here.

Look at this page http://browningmgs.com/FN/04_parts.htm

I'm building the modele 1932 (top RSP picture) I'm calling the RSP in your post a modele 1938. Do you have information that does not agree with this web site's definitions? I know some call the weapon I'm building an FN38 because that date is engraved on the LSP. And then call the FN38 an FN39.

Anyway, the RSP in your post is my next project. I have a kit to go with it.

I want to confer with you before riveting. As you pointed out, I riveted the wrong bottom plate on my last FN38 build. Got to re do that. HATE when that happens. Also need to see what Dolf has on the subject.

Karl
 

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For the 32 you have the right design, but in your first post you show a 38 LSP so I assumed that was the LSP for this build. If you were just using it for dimensions then please ignore my incorrect assumption. The series model nomenclature is a cluster, my model 32 from Kris is marked model 38. Maybe I'll mark my 38 as a 32 so I have one of each.
 

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Discussion Starter #13 (Edited)
For the 32 you have the right design, but in your first post you show a 38 LSP ...

DOH, can't sneak anything past you:lol:

Yep, I measured up both hoping to run them at the same time. But the FN38 RSP is considerably different than the FN32. In fact its nearly an FN30 with the relief or lightening cuts.

One thing I discovered is the backplates aren't interchangable between the FN32 and all the other FNs (30,38 model 52). Still thinking, but it seems modifying the 32s to fit all the other FNs is the way for me to go. Hedgehog gave me a vertical buffer back plate (belongs on a 32) modified to FN30 size with spade grips for the 38 kit I bought from him. I've got extra horizontal buffer back plates to fix this issue.

Karl

<follow up>

did some more checking. The top plate on the FN38 is 90 thous longer than the FN32. Same as length difference in side plates. So, the extra length is all due to the difference in back plates. Turns out one of the FN32 kits has a FN38 top cover. The same kit had the FN38 bottom plate that I was short on for my first FN38 build. I have just now figured out the last FN32 kit I bought was actually an FN38 with just the FN32 side plate.

Karl
 

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Discussion Starter #14
If you all like CNC machine porn, I posted pics of the machining over on hobby machinist forum
http://www.hobby-machinist.com/threads/fn32-right-side-plate.43543/#post-376340

Sorry, too much work to repeat here.

here's the first receiver test fit. I'll re double check everything and then make a few spares. Never know, might need to build another FN32 someday.

This project will likely go dormant for a while. I'm going to do the FN38 receivers next. Then figure how to get all the engraving done before building
 

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Discussion Starter #15
Engraving???

Does anyone have info on the correct engraving for the FN32? and the FN38 for that matter.

My mill has too much TIR to engrave (breaks the tool) I have read about electro etching. that's the current (joke here) plan. Turns out I have three scrap receivers made. Didn't see an issue with the return spring location on part one :jedicrying: , so I have practice parts.
 

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Discussion Starter #16
FN32 vs FN38 part differences

This build is forcing expertise on the minor, but important differences between the FN32 and FN38. I am also learning that these kits are a mis mash of parts from both models. Apparently this can be traced to the importer, IMA. So if you buy a kit, be fore warned.

Any way, the pic shows FN38 parts on the top and FN32 on the bottom.

green arrows shows a boss on the FN38 backplate. Also the slots on the FN32 backplate are narrower and do not fit the other FN machine guns.

Yellow arrows show a pin on the FN32 lockframe. No pin on the FN38 frame. Instead it is cut to meet the boss on the backplate. So, there are also no slots on the FN38 LSP and RSP to hold the lockframe. I'll mention here the FN38 RSP and LSP are 0.090" longer than the FN32. Same measurement differences in the top cover.

Red arrows show a larger return spring catch on the FN32. Sames difference in the RSPs. This is backward from the info on my bible site, browningmachineguns.com
 

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Wow, Your 32 box looks great. Good job recreating a very difficult side plate from scratch. I wish I had a fraction of your machining talent, unfortunately I am just an assembler and tinker.
 

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That is a good looking project, I will say you have two things I dont. Skill and a mill lol. Congrats on a fine project.
 

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Discussion Starter #19
Guess I'm getting a bit lax about keeping my thread updated...

I decided to also make the RSPs for the FN38 before moving on. part 1 on the 38 should come off the mill next week. I'll try and post some pics of that operation.

Karl
 

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Discussion Starter #20
I'm feeling pretty full of myself right now...

Part one on the FN38 just came out of the CNC mill. Its in spec! That just don't happen on a complex part like this where you're making your own print by estimation from other parts on the weapon.

Still got a backplate and return spring slot to cut - no big deal. I wasn't going to bother on the first part.
 

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