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Chassis Build

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jbolt

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#1
This will be a build log for a tactical rifle chassis build. I figure since most of the manufacturing will be done on my CNC converted PM-932 I would post it in the CNC forum.

This is the CAD model I did in Solidworks. The chassis is loosely based on the Remington MSR. This is setup for a Rem 700 short action receiver.

JTAC-7000.png
JTAC-7000 Folded.png

I started with the easiest parts, the butt pad mount and slide.

The mount has ops on both sides so those were done in the vise. The perimeter was done by bolting it to a fixture held in the vise. The slide was drilled then bolted on the same fixture to do the perimeter and dovetail.

Tool paths in HSM Express.
Butt Pad Mount Tool Paths Small.png

Completed slide on fixture.
20160821_102425.png 20160821_102436.png

Completed mount and slide.
20160821_102829.png 20160821_102910.png 20160821_103637.png

The parts get more complicated from here so figuring out the work holding will be a challenge.
 

Metal

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#2
ooh neat looking, is this an "only for me" project or will you eventually make the file avail? :)
 

jbolt

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#3
ooh neat looking, is this an "only for me" project or will you eventually make the file avail? :)
We'll see how it comes out first. :cautious: This is the 5th revision just in CAD. The final version may have some changes depending on how the parts come out or difficulty in machining.
 

jbolt

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#5
I got the stock pivot block done today. I tried to take a time laps video but the lighting on the mill washes out the image and the flood coolant doesn't help. I'll try with the lights off on the next part.

I had a couple of hiccups. When I first designed the part I had the corner screw holes and counter bores too close to the edge. I moved them in but did not catch that the 1/4" spot drill would rub the side so it left a mark. The other issue was I made the rough stock a little too large in one direction and it cut one of the round overs a little too deep. Those are minor blemishes that will be hidden in the pivot well of the stock plus I will be painting everything so it can be fixed without remaking the part.

The part took 11 different tools over 5 separate setups. Total machining time was about 50 minutes including setup changes.

Part in CAD, with tool paths and finished.
Pivot1.png Pivot2.png IMG_0002.JPG
 

countryguy

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#6
AWESOME!!! My Kid is going to flip. He's a few years away from this level of competence but hopes to be able to do things like this. What material are you using for the parts? Mix of metals? Alu... any Alloys or Titanium (teasing) to come. Will be watching Sir!

Thanks for the build post.
JJ
 

Billh50

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#7
Very nice looking. I watched a build before on a mosin nagant that looked incredible. I was wishing he would have released his plans but he didn't. I have a mosin that someone had cut down a bit and would have loved to make something like he did. I think your build will be even more intriguing to many. Good Luck with the build.
 

jbolt

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#8
Thanks JJ & Bill!

Next part is the butt stock. 13 tools, 7 setups, 22 tool paths, plus 1 fixture. The first 5 setups were done in the vise including the top, front, rear, left and right sides. The last 2 setups were done on a fixture held in the vise. These were the right and left contours and corner rounding. The corner rounding was done in a 3D tool-path with a 3/16" ball end mill. The corner rounds took 21 passes to complete. The fixture was setup to be able to flip the part and use the same work offset. The part was held to the fixture with two 8-32 screws through the clearance holes in the part and a plate at the front that used the already drilled holes for mounting the pivot block. I still need to do the narrow slits in the top and rear but I need to get a smaller slitting blade and arbor. Overall I am very pleased with how this came out considering all the different setups and I managed not to to screw up a tool path.

Tooling

ButtStockTooling.png

CAD and CAM
ButtStockLeftCAD.png ButtStockLeftCAM.png ButtStockLeftonFixtureCAD.png ButtStockLeftonFixtureCAM.png ButtStockRightonFixtureCAM.png

Completed part
ButStockLeft.png

Completed part with Pivot block attached.
ButStockRightwPivot.png
 

jbolt

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#10
Here is part 1 of several showing the machining of the butt stock. I'm still getting used to this camera. It seems to stop recording after 48 minutes and has to be restarted so I missed some operations. I'm no video editor so these are just the raw footage speed up 16x.

 

09kevin

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#11
Hi Jay. Nice looking parts!

Kevin
 
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jbolt

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#12
Thanks Kevin!

Two more videos capture the majority of the machining process. Sorry for the dead spot in video 2 as I got called away and am too lazy to edit it out.

 

bpratl

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#13
Jay, that is some very impressive design, setup and machining. Bob
 

jbolt

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#14
Thanks Bob!

Rats my lathe delivery was put off unit tomorrow so I had some time to run another part. This is the hand grip mount. The grip is an AR-15 type.

This was a fun part to do. Just modeling the part challenged my feeble knowledge of Solidworks and then came the CAM. I tried some new 3D strategies and it worked out well.

GripMountCAD.png GripMountCAM.png

This part took 5 setups, 11 tools and 31 tool paths.

GripMount01.png GripMount02.png GripMount03.png GripMount04.png GripMount05.png GripMount06.png GripMount07.png GripMount08.png
 

Sendit

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#15
Hello. The recoil pad how did you go about modeling it/measuring to get the profile so perfect ?


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09kevin

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#16
Looks good Jay! I noticed that you were playing with the 4th axis in another post, have thought about using it on some of these parts?

Kevin
 

jbolt

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#17
Hello. The recoil pad how did you go about modeling it/measuring to get the profile so perfect ?


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I traced the base of the recoil pad, scanned it to a bitmap file and then imported it into Solidworks. The bitmap lines on one half of the profile are traced with a spline line, mirrored and then a scale is applied to get it to the proper size. The 3D model is a simplified version of the actual part. I just need the basic dimensions for sizing of the other parts. The same base profile for the but pad is used to create the profile for the adjustable mounting plate.

ButPadSplines.png
 
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jbolt

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#18
Looks good Jay! I noticed that you were playing with the 4th axis in another post, have thought about using it on some of these parts?

Kevin
The barrel guard and the mount for the barrel will have operations on the 4th axis. Mostly indexing moves for 2D tool paths. I still need to finish the stepper motor mount for my rotary table and get the post processor modified before I can try any 4th axis work. I have figured out how to do the CAM so that part of the puzzle is good to go.
 

Metal

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#19
Neat stuff, I'm still learning how to fixture stuff properly so it is extra interesting to me.

Turns out I can't indicate to save my life yet >.>
 

jbolt

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#20
I made a little more progress. I have started on the maim part of the stock.

StockCAD01.png

The first three side are done in a vise. The front, top and left sides. The first was to drill the holes in the front and then run the top.

Tool paths for the top.
StockCAD02.png

Top completed.
Stock01.png

Next was the left side.
StockCAD03.png

Left side ops completed.
Stock04.png
 

jbolt

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#21
The receiver stock is done. I had a few anomalies with some of the tool paths where the cutter skipped over some of the details during the 3D passes. It's kind of strange where most finished dimensions are within a few thou which I think is good considering there were tool paths on 5 of six sides but there are a few that were 10 to 20 thou off, all on the 3D tool paths. Part of the path would be perfect and another part would be slightly off. I have some backlash in the system I need to take care of and it really shows in some of the blend lines.

I also discovered the 3D CAD model of the receiver I got from a friend wasn't modeled correctly. The important dimensions were there but the taper at the rear of the receiver is way off and the slot for the bolt handle is not deep enough. I'm going to try and recut the taper. Hopefully it comes out okay. I'm still trying to figure out how to use extra long end mills without leaving chatter marks.

Stock05.png Stock06.png Stock07.png
 

Bill Gruby

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#23
I normally am not intrigued by CNC machining. It does not do much for me, but this project is amazing and well documented. The videos are awesome. Thank you for taking the time to post this.

"Billy G"
 

TomS

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#24
I'm not into guns but that is a beautiful piece of machining.

Tom S.
 

jbolt

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#25
I was able to recut the back taper to more closely match the receiver and recut the pocket for the bolt handle so now the receiver stock is done.

Next is the part that mounts the barrel guard to the stock.


Solidworks Model
BarrelGuardMount06.png

Rear side tool paths
BarrelGuardMount07.png

2" x 3" x 2.5" block bored, turned and here getting the taper cut.
BarrelGuardMount01.png

Bolted to the fixture ready to machine. Normally I would hold a part like this in a soft jaw but it needs to be milled on both ends so the same fixture can do both sides. That's a 1/2-13 bolt holding it in place.
BarrelGuardMount02.png


Drilling and milling completed. I normally model the part and the fixtures and then do the CAM from that assembly. I can then run stock simulation to look for clearance or tool path issues. Because I did the fixtures on the lathe as they were simple I did not bother to model it. Well that bit me. I failed to adjust the default clearance height for one of the 3D contouring operations and when it finished it went to the safe Z that was too low and then to the starting position for the next tool which was across the part. That cost me a 1/4" carbide ball end mill when it tried to rapid through the steel bolt head at 50 ipm. Ugh!
BarrelGuardMount03.png

Ready for the front side.
BarrelGuardMount04.png

With all the roughing work I have done this week the cutting fines are wreaking havoc with the coolant pump check valve and I keep loosing prime on the pump. I need to sort that out before continuing.
 

sgisler

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#26
Very nice work! What are you using for CAM?


Stan
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sgisler

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#28
Thanks! I wondered if that's what it was. I'm just getting my feet wet in Solidworks (was using Fusion but had to have sheet metal, so bought SW).
Love the project, gives me some ideas!


Stan
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