Umarex Notos CRK Review

[subscriber]

First new insert request ready for publication:  1 inch OD by 5 inches long

It is the height and OD of the part that takes so long to print, rather than 100% infill.  I have made the wall thicknesses as thin as I dare, to increase internal volume, and to save print time and material; and to reduce weight.  So, less than 100% infill may be asking for trouble.

The STL print file is attached below:

[Firewalker]

Here we go! 

Thank you Subscriber!

Ready, mike?

[miksatx]

Here we go! 

Thank you Subscriber!

Ready, mike?

loaded for a early morning start.

[subscriber]

Dave,

I am busy with the extended version.  The bit where I need help is the location of the pin holes, so I can place the bosses to receive them in the correct location.  I have assumed locations, based on all the info you have provided, but could be off.  The images below show what I have.

The idea is to leave the pin holes blank, but to provide some external features so you can rotate the insert to the correct position before drilling the pin holes.  One way is to leave dimples on the outside. 

I assumed the pins are 2 mm in diameter, based on your images.

I have provided as many reference points to help you help me, as possible

Please comment so I can get this tricky aspect done.

Images below...

[subscriber]

Dave,

Extended Notos insert below has an overall length of 8".

You will be glad to hear that I made the need to know the exact pin placement more or less irrelevant: 

I placed a cone in such a position that the wall thickness completely absorbs the bosses for the pins.  In other words, the rotational orientation of the tube does not matter when the pin holes are transfer drilled from the outer casing. 

Just take a look at the dimensions provided and "pencil line image" where the bosses were, and see if there is enough material around where the pin holes would be in my CAD model.  Then compare to your own measurements. 

If I am off by several mm, then moving the cones to suit may be required.  I am going to assume that the design shown below is a workable solution, so I am attaching the STL print file.

In fact, I am attaching two print files:  One version has 8 expansion chambers and the other 7.  This is in case the original first chamber ahead of the insert has been removed by making the casing hole deeper, and then using all that depth for the insert.  You could have Mike print both, then compare for sound and grouping ability.   

The 8 chamber version has the pellet travel a shorter distance before it is in the "shadow" of the second air stripper.  This may, or may not matter in practice.  If you had not broken the 4 chamber 3" insert, its performance against the 5 chamber insert would help predict the performance of the longer one.

The last image compares the 1 x 5" insert I posted a few hours ago, next to the 7 and 8 chamber extended insert versions, for comparison.

[subscriber]

My concern about the following would be zero, if the insert cone and muzzle crown were perfectly concentric.  If there is any doubt about it, then the modification suggested below might be smart.  I could do it in CAD, but right now, I am speculating.

Question for Dave:

With your deeper casing cavity and longer insert, does the barrel muzzle contact or come close to the flat end of the insert cone?  Image below might show what I am thinking.

If what amounts to the first air stripper contacts the muzzle or is less than 3/4" away I advise that you open the hole in the insert cone to almost match the barrel OD.  Else, the air would be deflected, but have no where to go as it leaves the muzzle. 

I think there is potential for that disturbed air to buffet the pellet; so rather stand off the first functional air stripper.  If my suspicion is right, the second air stripper would become the first functional air stripper; if you remove the first air stripper from the small end of the insert.  You can core it out; or cut it off.

If there an open air space between the end of the insert and the end of the cavity, near the muzzle, then having the first air stripper 1/2" away from the barrel muzzle should be OK.

[subscriber]

So, rather than speculate and wait to provided an open end insert print file, I am anticipating that you will want that, Dave  (if not, then no harm done). 

So, the attached 7 and 8 chamber insert design STL files both have a 16 mm diameter hole on the end of the cone.  Everything else is the same as the above insert versions.

[Firewalker]

I'm at work right now and will have 1 hour to measure and post the measurements.

I will try to read through the posts today and get "exact" pin locations, pin diameter and length.

Thank you and Mike for your continued diligence!

[Firewalker]

The last ones shown with very little chamfer will be preferred. I intend to bore out the walls to 1" all the way to the base where the barrel is mounted, I forget what I posted for depth.

I will remove the step and make the whole housing 1" ID.

I will make a jig for the pin holes from steel tubing so locations are repeatable.

[subscriber]

Dave,

There is also the question of the shoulder location, as you will be leaving out the stock endcap.  I moved the insert shoulder 6 mm to account for the cap, but do not have a complete picture of how things go together.

My second attempt seeks to make the exact pin hole location more forgiving.

Now, for unsolicited advice:  Do not use a countersinking tool to recrown the barrel.  It will raise a huge burr and here is the kicker; unless you indicate off the bore, using the OD of the barrel in a lathe may result in an eccentric crown.  If a conical crown is eccentric the cone will lean over and be obviously asymmetrical. 

Rather, use a very sharp cutting tool with a narrow tip, held in a stiff boring bar, and skim the muzzle flat; facing from the inside towards the outside.    Then, use a brass ball lap of appropriate diameter to just break the edge on the lands and grooves. 

Working into the 6.5" deep "can" won't allow you to orbit the lap very much.  If you plunge the lap rather than orbit it, the lap will wear into a nub, that will enter the bore and round over the edge of the bore, rather than create a clean transition.   

If the insert housing is removable, that would make the crowning job easier.  But if it is glued, pressed or molded on, getting the housing back with integrity may be tricky.  It may be pinned on, in which case removing it might be useful.

Be careful not to improve something that is not broken until it is...

I like to help, but do not want to facilitate and encourage Notos mutilation.  Especially not due to either of us being in a hurry.  My goal is to give you something you can use; even if you have to modify the insert.  Not to encourage you to take a step that you will regret later.

I was wondering if keeping the insert socket stock and making just an extended insert for it is not the safe way to go?  Increasing the insert diameter from 24 to 25.4 mm does not gain a lot of volume.

I would just add a more deliberate air stripper cone to the conical end, so you keep the primary blast chamber that is stock, as designed to work with the original parts.

Anyway, I don't want to ruin your fun.  I also don't want to seem like I doubt your skill.  I know nothing about it.  It is just that I normally have very clear interface dimensions in mind before committing to a design.  Also, know from experience that it often requires a few iterations to get 3D printed parts to fit just right.  And we don't have much time for that, unfortunately.

[subscriber]

I did a scale layout sketch to determine the ideal crown lapping ball diameter.  This assumes a tangent at the caliber groove diameter, at 45 degrees. 

McMaster brass screw https://www.mcmaster.com/92453A199/ is shown with a scale 5.5 mm groove diameter and tangent lines at just over 50 degrees - "flatter" than 45, so OK; considering the ball will wear a little during the crowning job.

Smaller screw: https://www.mcmaster.com/92453A153/ produces a less than 45 degree tangent, at 42.7 degrees.  I would not go smaller than this screw head size, although the head OD can be reduced as that does not contact the crowning job. 

The problem is screw stem (or extension) clearance to enable orbiting while lapping.  Unless you remove the LDC housing from the barrel.

[Bluesman]

I want to take the hammer out and not sure of one thing. Is it safe to remove this bolt with the cylinder under pressure?

[avator]

Are these guns really loud enough to require an after market silencing system?

[Bluesman]

Are these guns really loud enough to require an after market silencing system?

Require, no in my opinion, but individual preferences and circumstances vary. Besides though, tinkering can be fun for it's own sake.

[avator]

Are these guns really loud enough to require an after market silencing system?

Require, no in my opinion, but individual preferences and circumstances vary. Besides though, tinkering can be fun for it's own sake.

Fair enough... I get the tinkering thing.

[stroo]

And my rural property becoming less rural quickly, is making me quite interested in the quiet aspect.  And yeah, tinkering is fun!   

[Firewalker]

Subscriber, it's a PGT live pilot crowning tool, I didn't post it that way because I was...

lazy

[Firewalker]

Dave,

There is also the question of the shoulder location, as you will be leaving out the stock endcap.  I moved the insert shoulder 6 mm to account for the cap, but do not have a complete picture of how things go together.

My second attempt seeks to make the exact pin hole location more forgiving.

Now, for unsolicited advice:  Do not use a countersinking tool to recrown the barrel.  It will raise a huge burr and here is the kicker; unless you indicate off the bore, using the OD of the barrel in a lathe may result in an eccentric crown.  If a conical crown is eccentric the cone will lean over and be obviously asymmetrical. 

Rather, use a very sharp cutting tool with a narrow tip, held in a stiff boring bar, and skim the muzzle flat; facing from the inside towards the outside.    Then, use a brass ball lap of appropriate diameter to just break the edge on the lands and grooves. 

Working into the 6.5" deep "can" won't allow you to orbit the lap very much.  If you plunge the lap rather than orbit it, the lap will wear into a nub, that will enter the bore and round over the edge of the bore, rather than create a clean transition.   

If the insert housing is removable, that would make the crowning job easier.  But if it is glued, pressed or molded on, getting the housing back with integrity may be tricky.  It may be pinned on, in which case removing it might be useful.

Be careful not to improve something that is not broken until it is...

I like to help, but do not want to facilitate and encourage Notos mutilation.  Especially not due to either of us being in a hurry.  My goal is to give you something you can use; even if you have to modify the insert.  Not to encourage you to take a step that you will regret later.

I was wondering if keeping the insert socket stock and making just an extended insert for it is not the safe way to go?  Increasing the insert diameter from 24 to 25.4 mm does not gain a lot of volume.

I would just add a more deliberate air stripper cone to the conical end, so you keep the primary blast chamber that is stock, as designed to work with the original parts.

Anyway, I don't want to ruin your fun.  I also don't want to seem like I doubt your skill.  I know nothing about it.  It is just that I normally have very clear interface dimensions in mind before committing to a design.  Also, know from experience that it often requires a few iterations to get 3D printed parts to fit just right.  And we don't have much time for that, unfortunately.

Printed parts are easily sanded to fit, the 1" ID and 5" depth gives anybody that wants to play with designs a generic starting point.

[subscriber]

Sounds OK on both points, Dave.

Carry on.

[kbstingwing]

anyone planning to put a drop block and carbon fiber bottle on the notos?