Using the holescreek straightening mandrel

[bladeworks123]

Well, I keep showing up here too late every day....

[holescreek]

I got all the mandrel sets done and decided I needed to bend another flat to use for trial fitting a part I'm working on in the shop. I bent the flat in the usual way and decided to try out one of the new sets as a form of quality control and figured I'd share the outcome.

Here's the fresh bent receiver straight out of the jig. Note the top radius isn't particularly round despite being pressed into a jig with the proper radius in the bottom. The raised portions are due to the slots that are stamped around the radius. I'll address them in a minute.:
http://i2.photobucket.com/albums/y29/Holescreek/Gunstuff/Mandrels/newmandrel060910005.jpg

Right out of the my jig, neither the bolt nor carrier will fit between the rails:
http://i2.photobucket.com/albums/y29/Holescreek/Gunstuff/Mandrels/newmandrel060910004.jpg
http://i2.photobucket.com/albums/y29/Holescreek/Gunstuff/Mandrels/newmandrel060910002.jpg

This photo shows the mandrel inserted all the way into the receiver. Once I got it started I was able to push in all the way in by hand. (Sometimes I have to pound the mandrels in with a dead blow hammer.) I have the rails in position so you can see how much work they have yet to do:
http://i2.photobucket.com/albums/y29/Holescreek/Gunstuff/Mandrels/newmandrel060910007.jpg

[holescreek]

Here is a view of the set-up in the press. I slowly make my way up and down the length of the rails making sure to keep the press ram over the squaring rails only. I found that pressing down directly over the plug welds is an easy way to mark my place. Even though the pressure is being distributed to both sides at once, I still flip the whole thing over and press from the other side:
http://i2.photobucket.com/albums/y29/Holescreek/Gunstuff/Mandrels/newmandrel060910011.jpg

As for those raised ares on the back of the receiver, a few taps with a body hammer will straighten them right out. (I used my mandrel for this, not the one that is already sold!). The last photo shows the finished radius.
http://i2.photobucket.com/albums/y29/Holescreek/Gunstuff/Mandrels/newmandrel060910013.jpg

http://i2.photobucket.com/albums/y29/Holescreek/Gunstuff/Mandrels/newmandrel060910014.jpg

[bladeworks123]

Holes, curious where you are ending up after your bend, on the overall height of the reciever measured from just in front of the FCG tabs to the top of the radius outside on top? And then also from bottom of mag well to the top?

[bladeworks123]

Hey, I just thought of something new,,,,You could also use your rail mandrels as a jig/guide for grinding the square edges under the scope mount lugs, in order to keep them in line to each other and at the same height. For you that would be easier done with your mill, but for guys without a mill that would work pretty good maybe...

[holescreek]

I got lost! I just saw that the thread was split and moved into the builders section. Serves me right for putting something that might be useful into a sale thread. Here's what I have:
http://i2.photobucket.com/albums/y29/Holescreek/Gunstuff/Top-4.jpg

I will assume that the anomaly with the dimensions in the middle are more related to the stamping dies than the bending since the ends are so much closer to your print dimensions.

[k98k792]

Yep,I split it up.
The way to do it here is to do the tutorial in a separate thread, and confine the selling of the jigs in the for sale thread. You can then link to the tutorial. We try to keep the for sale threads from turning into multi page chat,or instructional threads.Also, useful information is not hidden,so to speak,in a thread that no one may read if you stop selling your mandrels,and have the thread marked SPF. Thanks

[holescreek]

I was just poking fun at myself. It's too easy to get caught up in a thread after info starts flowing to realize that it's heading for a waterfall.

[bladeworks123]

:icon_biggrin: Haaaa! I like the way K started out with the post about me showing up late every day..................

Thanks Holes!!! I think what you may find is that the bottom below the rails in the rear has a tendancy to close up and be a little narrow sometimes. I have the same exact problem, which I have gotten around by squaring up the bottom rear and blocking it first and then squaring my rails. It lets you set the FCG square to the receiver rather than having to have it drop in the front a bit.

[Buddymack]

Could something like this also be used to true up a receiver from something like out of a Century Arms MFG rifle?
It would seem like it would, maybe help cut back on that bolt drag if it was more true.

[bladeworks123]

Could something like this also be used to true up a receiver from something like out of a Century Arms MFG rifle?
It would seem like it would, maybe help cut back on that bolt drag if it was more true.

I'm sure it would,,,,maybe Holescreek can testify to that, but it seems like a perfect answer to truing up a receiver,,, newly bent or poorly bent, either one.

[holescreek]

I have used mine on two century rifles. First one was kind of scary for a couple of reasons.
First, it (the receiver) was pressed very narrow at the factory making it hard to get the mandrel started. It can obviously only be inserted until it hits the trunnion, leaving a couple of inches hanging out the back. When I pressed on the squaring rails I had to let off the pressure a bit on the ejection port end of the receiver for fear of crimping the back end of the cocking tube, but it all worked out.
Second, Not having used the mandrel on a finished rifle I wasn't sure how easily it would come off. Smacking the back of the mag well on a fresh receiver with a plastic hammer is one thing, on a finished rifle you have to be careful not to damage the mag well.

I found on one of the century cetmes that they had hammered the lower part of the receiver where the tabs are inward (only on one side), presumably to make the FCG fit easier. It was hard to tell it was bent until I had the mandrel in as it gave me a reference surface to view. I used a brass hammer to tap the edge of the receiver back where it should have been, slid the mandrel out and the bolt moved freely. I didn't even use the squaring rails. By collapsing the tab area in they had twisted the receiver enough that the bolt was dragging on the rails.

One of the century cetmes belongs to a member of this board (Airmedic). His did not have the bent tabs, just a very tight receiver. He also had a bent ejector which caused his bolt to stick back. We got it all straightened out and welded one of Turbo's pic rails on. Last I heard it was shooting like a champ.

[Buddymack]

It is what I was kind of thinking that without something like that you can get sort of lost on reference and depend too much on the eye, something that if done were I work can get us into trouble...but dang that mandrel looks good! I am new to this so what models would it be good for?

[holescreek]

what models would it be good for?

I'm not sure really, I have only used it on 91 style actions. I'm told that the MP5 uses the same internal shape but haven't bent one up myself. Bladeworks or another HK guru would know whether the other actions (93?) are the same shape.

All of my personal builds have been cetmes. I have assisted in a couple G3 builds as far as the bending and welding but most of the other 16 or so have been cetmes.

I'm not planning on making any more mandrel sets anytime soon. Too many of my own projects are lagging behind. I believe I read where rpmfly2 was thinking of renting his out. -Mike