I've done some searching looking for the answer to my rather specific question and have yet to find what I was looking for. I'm a young gunsmith and currently in machine tool school for cnc operations and programming so I have access to the vertical machining center every day. In the very near future I will be inletting a B&C stock for Badger DBM. My question is how/where do you guys that CNC inlet for DBM index the stock? I have thought about turning some pins to fit snuggly fit the stock bolt holes and use them to align the stock along the x axis. Any input would be very much appreciated! Thanks!
Gunsmithing CNC Inletting for DBM question.
- Thread starter tstevens
- Start date
Re: CNC Inletting for DBM question.
Think your on the right track. I would add a horizontal bar to those pins/dowels by weld or thread so that it sits down into the stock then you can indicate across that bar. Now your mount holes are perpendicular to the cut.
Most are cut pretty crude, by eyeball or rough level. They still seem to work ok.
Think your on the right track. I would add a horizontal bar to those pins/dowels by weld or thread so that it sits down into the stock then you can indicate across that bar. Now your mount holes are perpendicular to the cut.
Most are cut pretty crude, by eyeball or rough level. They still seem to work ok.
Re: CNC Inletting for DBM question.
Here's what I did:
I machined a base plate from cast 6061 stock. I stuck a hardened drill bushing at my X0/Y0 position so that the coax indicator would track nice. I then machined a track that a "puck" can slide in back and forth. It also has a hole for aligning the front action screw hole. This way I don't have to drill a bunch of holes in the plate for various length receivers.
The hole with the drill bushing is for the tang screw hole. All my inlets use this as X/Y zero.
For me its pretty simple. I use G56 as the designated offset. The fixture just plops onto the deck plate and locks down with 2 1/2-13 cap screws. All my offsets for tools are preset.
I drop the stock onto the fixture and orient it with two 5/16" pins that register through the pillar holes and into the drill bushing and puck. Clamp it up and I'm set.
Easy stuff and all the programming is written to perform all the operations in one setup. No rotating the stock to machine the guard bow portion because I use a small diameter tool (to minimize corner swarf) and just do a 3 axis move.
TIPS:
If your stock is pillar bedded your going to find that it wants to chatter when you transition from wood/fiberglass to AL/SS.
There's ways to get around this. I helically bore the pillar using a 1/2EM first and bore the pillar down to where its .025" above its finished height. This way my tool isn't contacting much of it when surfacing/qualifying the height.
Next, and this is kind of hard to explain so bear with me.
Naturally you want to climb cut whenever possible. Its a better finish and much more efficient. There are exceptions though and this is one of them.
The grip portion of the stock isn't supported. The back half of the stock is stuck out in space essentially. When you add the bow feature in the stock you climb cut all the way around. Think about what's happening though.
At first your moving in a X and POS Z move. Then you go into an arc and start to come back DOWN on the back side. When you do this your PLUNGING into the pillar slightly. This creates a bad finish because the stock flexes slightly as it begins to sink in the Z axis. Once you get off the harder pillar material the stock "pops back" slightly and you end up with a divit right in front of the rear pillar as the tool plunges deeper into the core material of the stock.
With a total rigid setup you might get away with this. Unless your clamping is very elaborate though it's a problem.
There's another way.
Just split the arc movement in half at the back of the guard bow feature. Lead in, cut to Y zero, retract, rapid to the opposite side start point, and conventional cut that side to the y zero position coming the other way.
Done like this the tool is always moving in the positive Z direction and surface finish greatly improves.
Also, floor metals are not created equal. They seem to fluctuate a bit. Program your stuff using either cutter comp or if your software supports it, use wear compensation. This is good for getting the slip fit we all like to see.
Hope this helps and great question! I wish there were more of them like this as it would start to show that the industry is evolving into the 21st century.
Good luck and welcome!
C.
Surface machining the radius so common on various floor metal designs. this way it matches the part.
CNC opens so many doors!
Here's what I did:
I machined a base plate from cast 6061 stock. I stuck a hardened drill bushing at my X0/Y0 position so that the coax indicator would track nice. I then machined a track that a "puck" can slide in back and forth. It also has a hole for aligning the front action screw hole. This way I don't have to drill a bunch of holes in the plate for various length receivers.
The hole with the drill bushing is for the tang screw hole. All my inlets use this as X/Y zero.
For me its pretty simple. I use G56 as the designated offset. The fixture just plops onto the deck plate and locks down with 2 1/2-13 cap screws. All my offsets for tools are preset.
I drop the stock onto the fixture and orient it with two 5/16" pins that register through the pillar holes and into the drill bushing and puck. Clamp it up and I'm set.
Easy stuff and all the programming is written to perform all the operations in one setup. No rotating the stock to machine the guard bow portion because I use a small diameter tool (to minimize corner swarf) and just do a 3 axis move.
TIPS:
If your stock is pillar bedded your going to find that it wants to chatter when you transition from wood/fiberglass to AL/SS.
There's ways to get around this. I helically bore the pillar using a 1/2EM first and bore the pillar down to where its .025" above its finished height. This way my tool isn't contacting much of it when surfacing/qualifying the height.
Next, and this is kind of hard to explain so bear with me.
Naturally you want to climb cut whenever possible. Its a better finish and much more efficient. There are exceptions though and this is one of them.
The grip portion of the stock isn't supported. The back half of the stock is stuck out in space essentially. When you add the bow feature in the stock you climb cut all the way around. Think about what's happening though.
At first your moving in a X and POS Z move. Then you go into an arc and start to come back DOWN on the back side. When you do this your PLUNGING into the pillar slightly. This creates a bad finish because the stock flexes slightly as it begins to sink in the Z axis. Once you get off the harder pillar material the stock "pops back" slightly and you end up with a divit right in front of the rear pillar as the tool plunges deeper into the core material of the stock.
With a total rigid setup you might get away with this. Unless your clamping is very elaborate though it's a problem.
There's another way.
Just split the arc movement in half at the back of the guard bow feature. Lead in, cut to Y zero, retract, rapid to the opposite side start point, and conventional cut that side to the y zero position coming the other way.
Done like this the tool is always moving in the positive Z direction and surface finish greatly improves.
Also, floor metals are not created equal. They seem to fluctuate a bit. Program your stuff using either cutter comp or if your software supports it, use wear compensation. This is good for getting the slip fit we all like to see.
Hope this helps and great question! I wish there were more of them like this as it would start to show that the industry is evolving into the 21st century.
Good luck and welcome!
C.
Surface machining the radius so common on various floor metal designs. this way it matches the part.
CNC opens so many doors!
Re: CNC Inletting for DBM question.
Wow Chad! I've read your post at least 10 times now trying to soak it all up. Now let me take a stab at relaying how I interpreted your instruction. What I gather is you have a fixture that you dial in on the mill bed then place the stock on. This fixture then holds the 5/16 pins for locating the stock. I understand why you helical bore the pillar down.
Now what I am still pretty lost on is where you talk about x and arcing positive z movements while machining the guard bow. Part of my problem is Im not positive of what the guard bow feature of the stock is either.
Also, are the dbm depths set from your fixture?
I sincerely appreciate everyone's help! Thanks
Wow Chad! I've read your post at least 10 times now trying to soak it all up. Now let me take a stab at relaying how I interpreted your instruction. What I gather is you have a fixture that you dial in on the mill bed then place the stock on. This fixture then holds the 5/16 pins for locating the stock. I understand why you helical bore the pillar down.
Now what I am still pretty lost on is where you talk about x and arcing positive z movements while machining the guard bow. Part of my problem is Im not positive of what the guard bow feature of the stock is either.
Also, are the dbm depths set from your fixture?
I sincerely appreciate everyone's help! Thanks
Re: CNC Inletting for DBM question.
Guard bow: Portion of the DBM that protects the trigger as it hangs down below the stock.
The feature in the stock would be a slot with a radius at one end. (closest to the grip)
Picture the stock upside down with the buttplate facing to your right as you stand in front of the machine. The entry point for your tool is where the magazine goes. You plunge in Z (neg) and begin moving in a +X direction. Because the stock is registered off its top edge (show line) and because the guard bow is made at an angle (typically 2.5 to 3.5 degrees) the tool needs to run in both the +X and +Z direction as you travel from magazine box to the rear guard screw. This machines the angle so that the bow registers flush.
Once you begin your arc movement you stop at the Y0 point. Tool retracts and you repeat on the opposite side. Only here your conventional cutting.
I use a presetter for tools. I made it and it's pretty ghetto but it works well enough. This way all I have to do is adjust the work offset Z height to bring all the tools down to the work plane of the part.
For floor metals I use the top of the fixture as my Z zero point. All the code is written with +Z values. (absolute programming. I usually don't use incremental stuff as its just too easy to get confused and really screw something up)
Whenever programming a new type of floor metal all I do is add the radius of the receiver (say a M700, it measures typically 1.350 dia) to the advertised pillar height requirement needed to set the part so that it functions correctly.
Say it states you need a .600" front pillar. I'd add .675 to .600 for 1.275. That's the height the pillar would end up being from the show line edge of the stock (or top of the fixture)
just repeat for the rear.
In a perfect world this would just drop in and run. It never seems to. There's a lot of fluctuation in exactly where receivers end up in terms of how they sit in the stock. There are variations in the floor metals, stocks, magazines, etc. With hinged floorplates for sporting guns you have more freedom/flexibility. The DBM systems are a bit more rigid in how they get fitted. A leaf spring and follower doesn't care if you alter the angle of the floor metal so that it runs dead nutz flush with the bottom of the stock. It'll flex and compensate accordingly. You can't do that with a DBM system though. If you try it the magazine will have issues when feeding. The outer chassis of the magazine needs to be at a right angle to the bore centerline. If you drop the nose too much it won't feed. Bullets will be inclined to hang up right under the feed ramp of the receiver. If you have the back side too far down the bolt will run right over the top of the cases and it won't feed.
With some DBM's I end up modifying them slightly. I try to have the parts fit well in the bottom of the stock without bedding them. Sometimes getting the part flush means the magazine is too close to the feedlips and it binds. In cases like this I just shorten the release lever till it all catches back up. It's better to modify this part because it will be more inclined to work with any magazine vs having to modify magazines individually.
What it all means is you want to set things up so that you can fudge individual portions of your program. Doing so saves time and allows you to tailor the fit to each stock you do.
Hope this helps.
C.
Guard bow: Portion of the DBM that protects the trigger as it hangs down below the stock.
The feature in the stock would be a slot with a radius at one end. (closest to the grip)
Picture the stock upside down with the buttplate facing to your right as you stand in front of the machine. The entry point for your tool is where the magazine goes. You plunge in Z (neg) and begin moving in a +X direction. Because the stock is registered off its top edge (show line) and because the guard bow is made at an angle (typically 2.5 to 3.5 degrees) the tool needs to run in both the +X and +Z direction as you travel from magazine box to the rear guard screw. This machines the angle so that the bow registers flush.
Once you begin your arc movement you stop at the Y0 point. Tool retracts and you repeat on the opposite side. Only here your conventional cutting.
I use a presetter for tools. I made it and it's pretty ghetto but it works well enough. This way all I have to do is adjust the work offset Z height to bring all the tools down to the work plane of the part.
For floor metals I use the top of the fixture as my Z zero point. All the code is written with +Z values. (absolute programming. I usually don't use incremental stuff as its just too easy to get confused and really screw something up)
Whenever programming a new type of floor metal all I do is add the radius of the receiver (say a M700, it measures typically 1.350 dia) to the advertised pillar height requirement needed to set the part so that it functions correctly.
Say it states you need a .600" front pillar. I'd add .675 to .600 for 1.275. That's the height the pillar would end up being from the show line edge of the stock (or top of the fixture)
just repeat for the rear.
In a perfect world this would just drop in and run. It never seems to. There's a lot of fluctuation in exactly where receivers end up in terms of how they sit in the stock. There are variations in the floor metals, stocks, magazines, etc. With hinged floorplates for sporting guns you have more freedom/flexibility. The DBM systems are a bit more rigid in how they get fitted. A leaf spring and follower doesn't care if you alter the angle of the floor metal so that it runs dead nutz flush with the bottom of the stock. It'll flex and compensate accordingly. You can't do that with a DBM system though. If you try it the magazine will have issues when feeding. The outer chassis of the magazine needs to be at a right angle to the bore centerline. If you drop the nose too much it won't feed. Bullets will be inclined to hang up right under the feed ramp of the receiver. If you have the back side too far down the bolt will run right over the top of the cases and it won't feed.
With some DBM's I end up modifying them slightly. I try to have the parts fit well in the bottom of the stock without bedding them. Sometimes getting the part flush means the magazine is too close to the feedlips and it binds. In cases like this I just shorten the release lever till it all catches back up. It's better to modify this part because it will be more inclined to work with any magazine vs having to modify magazines individually.
What it all means is you want to set things up so that you can fudge individual portions of your program. Doing so saves time and allows you to tailor the fit to each stock you do.
Hope this helps.
C.
Re: CNC Inletting for DBM question.
Thanks for the extra information!
Are you able to get the bottom metal on most dbm systems to flush up with the bottom of the stock? In doing so does the box (I don't know what else to call it) on the bottom metal that surrounds the magazine allow plenty enough room to flush the bottom metal without running the assembly as well as the magazine into the bottom of the action?
I was going to ask why a guy couldn't build a fixture set at 2-3* to match the belly angle of the stock but I would imagine the front pillar and front tang on the bottom metal is machined parallel to the stock.
So this leads me to believe the trigger guard area (rear 1/2) of the bottom metal is all machined at the same angle in relation to the front half of the metal.
I was really hoping there wasn't any 3D milling in installing these because as of right now I have to write my program longhand. Oh well, it'll be good practice.
Thanks again for all the help, I'm positive I'll have more questions in the near future.
Thanks for the extra information!
Are you able to get the bottom metal on most dbm systems to flush up with the bottom of the stock? In doing so does the box (I don't know what else to call it) on the bottom metal that surrounds the magazine allow plenty enough room to flush the bottom metal without running the assembly as well as the magazine into the bottom of the action?
I was going to ask why a guy couldn't build a fixture set at 2-3* to match the belly angle of the stock but I would imagine the front pillar and front tang on the bottom metal is machined parallel to the stock.
So this leads me to believe the trigger guard area (rear 1/2) of the bottom metal is all machined at the same angle in relation to the front half of the metal.
I was really hoping there wasn't any 3D milling in installing these because as of right now I have to write my program longhand. Oh well, it'll be good practice.
Thanks again for all the help, I'm positive I'll have more questions in the near future.
Re: CNC Inletting for DBM question.
Most fit pretty close. It largely depends on the stock being used. The companies that use multiple molds for the same model seem to have slight variances, but were talking small amounts that can easily be adjusted for with some elbow grease and a sanding block. (assuming your willing to paint the stock. For us that's easy as we paint all the guns we build)
Even with the 3axis moves its still pretty simple. Its just G1's and G2's/G3's. You'll have some I's and J's in there as well. Just know that with some floor metal systems (Like the Badger/PTG DBM) the rear pillar pad is machined parallel to the bore/show line edge. This makes it easier as you don't have to include the 3axis move across the arc. It's just a X/Y start/endpoint with a radius thrown in.
In the past my older software versions would support/post a 3axis arc movement so I had to generate them as splines. IE short line segments that form an arc. This makes for really busy code and the need to really slow down feedrates as splines tend to make the machine behave like Michael J. Fox. (bad joke, sorry-not really
)
Most fit pretty close. It largely depends on the stock being used. The companies that use multiple molds for the same model seem to have slight variances, but were talking small amounts that can easily be adjusted for with some elbow grease and a sanding block. (assuming your willing to paint the stock. For us that's easy as we paint all the guns we build)
Even with the 3axis moves its still pretty simple. Its just G1's and G2's/G3's. You'll have some I's and J's in there as well. Just know that with some floor metal systems (Like the Badger/PTG DBM) the rear pillar pad is machined parallel to the bore/show line edge. This makes it easier as you don't have to include the 3axis move across the arc. It's just a X/Y start/endpoint with a radius thrown in.
In the past my older software versions would support/post a 3axis arc movement so I had to generate them as splines. IE short line segments that form an arc. This makes for really busy code and the need to really slow down feedrates as splines tend to make the machine behave like Michael J. Fox. (bad joke, sorry-not really
)Re: CNC Inletting for DBM question.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: C. Dixon</div><div class="ubbcode-body">Whenever programming a new type of floor metal all I do is add the radius of the receiver (say a M700, it measures typically 1.350 dia) to the advertised pillar height requirement needed to set the part so that it functions correctly.
Say it states you need a .600" front pillar. I'd add .675 to .600 for 1.275. That's the height the pillar would end up being from the show line edge of the stock (or top of the fixture)
just repeat for the rear.
In a perfect world this would just drop in and run. It never seems to. There's a lot of fluctuation in exactly where receivers end up in terms of how they sit in the stock.</div></div>
I'm guessing this is part of why you fill stocks and make a nice flat show line plane to work from.
I find that most stocks don't have enough of a flat plane on top to work from that I always have to fudge with them a little bit when getting fixtured.
I have a 0.675" radius 700 bottom metal inletting fixture around here somewhere that I started on that actually raises the show line up slightly above the fixture plate to allow the show line variance to hang down so I am just indexing the bottom metal inlet location FROM the topside inlet.
Then I know where my pillar heights are at and I do the inlet using RRcode on the manual mill with a DRO...
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: C. Dixon</div><div class="ubbcode-body">Whenever programming a new type of floor metal all I do is add the radius of the receiver (say a M700, it measures typically 1.350 dia) to the advertised pillar height requirement needed to set the part so that it functions correctly.
Say it states you need a .600" front pillar. I'd add .675 to .600 for 1.275. That's the height the pillar would end up being from the show line edge of the stock (or top of the fixture)
just repeat for the rear.
In a perfect world this would just drop in and run. It never seems to. There's a lot of fluctuation in exactly where receivers end up in terms of how they sit in the stock.</div></div>
I'm guessing this is part of why you fill stocks and make a nice flat show line plane to work from.
I find that most stocks don't have enough of a flat plane on top to work from that I always have to fudge with them a little bit when getting fixtured.
I have a 0.675" radius 700 bottom metal inletting fixture around here somewhere that I started on that actually raises the show line up slightly above the fixture plate to allow the show line variance to hang down so I am just indexing the bottom metal inlet location FROM the topside inlet.
Then I know where my pillar heights are at and I do the inlet using RRcode on the manual mill with a DRO...
Re: CNC Inletting for DBM question.
Do the common DBMs taper on the outside of the mag box? I've only done an Atlasworxs and it's a pain because of the taper. I just shimmed the sides of the stock to match the angle with the x axis for the initial cut. I still had to fill with a little devcon.
Also mentioned, the trigger guard area; on the HSP stock I did it, starts to curve toward the grip about the middle of the guard loop. I didn't bother sanding this down as it's barely noticeable.
Do the common DBMs taper on the outside of the mag box? I've only done an Atlasworxs and it's a pain because of the taper. I just shimmed the sides of the stock to match the angle with the x axis for the initial cut. I still had to fill with a little devcon.
Also mentioned, the trigger guard area; on the HSP stock I did it, starts to curve toward the grip about the middle of the guard loop. I didn't bother sanding this down as it's barely noticeable.
Re: CNC Inletting for DBM question.
It sorta depends on the fixturing.
I do block sand the showline to try and qualify it. Most are pretty good, but sometimes they are twisted up pretty bad. I get it close, then just roll with it.
In my case I have a "setup bar" that goes into the mill. It's touched off just like all the tools are to the presetter.
From there is a simple G43 move. G43H16G90G0Z0.
G43 calls up the tool offset. H determines which tool (16 in my case) G90 signifies absolute dimensioning, G0 is the rapid move, and Z0. is the position.
The bar rapids down to .675" above the fixture. I pull the stock up to the underside of the bar and clam up the jaws of the fixture. Now the stock is parallel in the horozontal plane. Orient to get the centerlines, determine the lug position (X0. in all my inletting programs) and run the cycle.
If the action is a 1.450 or bigger receiver I adjust my G54 height offset accordingly. (the .675" value) .675 is the radius of most receivers. This way I can set the action on top of the vice jaw and imagine how its going to look in the stock once inletted. It gives me an early indication if the tang is going to cooperate or not. Also lets me check trigger positioning based on my X zero location.
For most M700 type receivers the rear trigger pin hole runs right in line with the trigger shoe location. Makes for an easy reference.
C.
It sorta depends on the fixturing.
I do block sand the showline to try and qualify it. Most are pretty good, but sometimes they are twisted up pretty bad. I get it close, then just roll with it.
In my case I have a "setup bar" that goes into the mill. It's touched off just like all the tools are to the presetter.
From there is a simple G43 move. G43H16G90G0Z0.
G43 calls up the tool offset. H determines which tool (16 in my case) G90 signifies absolute dimensioning, G0 is the rapid move, and Z0. is the position.
The bar rapids down to .675" above the fixture. I pull the stock up to the underside of the bar and clam up the jaws of the fixture. Now the stock is parallel in the horozontal plane. Orient to get the centerlines, determine the lug position (X0. in all my inletting programs) and run the cycle.
If the action is a 1.450 or bigger receiver I adjust my G54 height offset accordingly. (the .675" value) .675 is the radius of most receivers. This way I can set the action on top of the vice jaw and imagine how its going to look in the stock once inletted. It gives me an early indication if the tang is going to cooperate or not. Also lets me check trigger positioning based on my X zero location.
For most M700 type receivers the rear trigger pin hole runs right in line with the trigger shoe location. Makes for an easy reference.
C.
Re: CNC Inletting for DBM question.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Gene Poole</div><div class="ubbcode-body">Do the common DBMs taper on the outside of the mag box? I've only done an Atlasworxs and it's a pain because of the taper. I just shimmed the sides of the stock to match the angle with the x axis for the initial cut. I still had to fill with a little devcon.
Also mentioned, the trigger guard area; on the HSP stock I did it, starts to curve toward the grip about the middle of the guard loop. I didn't bother sanding this down as it's barely noticeable. </div></div>
With a manual machine it certainly does present unique challenges when cutting tapers and inside radius features. Back when I had to do it this way I chose to leave the part rigidly fixtured. One setup.
What I did was draw the part and then figure a stepover tool path that I could manually run to. Typically with something like a .05" stepover. This way I could just write positions down in a spiral notebook and just bang away at the handles while watching the DRO. It took awhile, but it worked well enough. I'd have to of course file/sand the scallops left from the tool.
Not saying its any easier or better, but this way I could do both sides at once without having to move the stock. Barrel channels were always the real pain in the arse.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Gene Poole</div><div class="ubbcode-body">Do the common DBMs taper on the outside of the mag box? I've only done an Atlasworxs and it's a pain because of the taper. I just shimmed the sides of the stock to match the angle with the x axis for the initial cut. I still had to fill with a little devcon.
Also mentioned, the trigger guard area; on the HSP stock I did it, starts to curve toward the grip about the middle of the guard loop. I didn't bother sanding this down as it's barely noticeable. </div></div>
With a manual machine it certainly does present unique challenges when cutting tapers and inside radius features. Back when I had to do it this way I chose to leave the part rigidly fixtured. One setup.
What I did was draw the part and then figure a stepover tool path that I could manually run to. Typically with something like a .05" stepover. This way I could just write positions down in a spiral notebook and just bang away at the handles while watching the DRO. It took awhile, but it worked well enough. I'd have to of course file/sand the scallops left from the tool.
Not saying its any easier or better, but this way I could do both sides at once without having to move the stock. Barrel channels were always the real pain in the arse.
