First Kit - Pak 40 Assembly Questions

[Kevin Williams]

I am building the PAK 40 kit and ran into some challenges.

(1) On stage 5. The Elevation gear and Slew gear, when I screw in the EJ0152 cover tight, the gears wont turn. If I keep it loose, it works, but rattles. Is there a trick to this?
(2) on stage 5. When I screw EJ0153 into the housing EJ0151 it wont allow the gear to turn if its screwed down tight. Is there a trick to this?
(3) on Stage 7. I couldn't figure out the rivets. Are these just glued in? if so, does the remaining part of the rivet stick through?
(4) On Stage 7. When connecting CQ0221 to the end. The M2.5 X8 button screws are too small for hole to thread in, so I see there are M2.5 Nuts that go with them. The holes are too close for the bottom ones to fit a nut. What should I do here? Glue?
(5) Stage 8. When trying to connect the breech CQ0148 together with CQ0145 it is extremely tight. I tried filing down a bit and help, but I need to grind down the parts more to truly fit. Is it expected to do this? Should I file / grind down the CQ0145 side so it fits easily?
(6) Stage 8. Putting together the breech block CQ 0149 and CQ0180 was difficult, as they didn't fit into CQ0148 easily. I had to really file it down to make it fit smoothly. I tried to put the breech block in after I joined the bigger breech pieces and this didn't seem to work if the Breech handle gear was installed. Do you have to join them all together before bolting down?
(7) Stage 8. Lots and lots of issues with breech handle and gears. Parts CQ0193 was too snug to fit in slot and holes would not accept 2x13 pin or HPC t0.25-20 gear. Also, HPC .25 - 2 gear wouldn't fit on pin. I tried drilling the holes bigger to allow them to turn and this seemed to help. Is that the correct way?

Any guidance would help. Apologies if I posted this in the wrong section.

Thanks,
Kevin

[Stephen White]

Kevin, there’s an unwritten skill engineers use known as “fettling” ie achieving a fit by making small adjustments. Start from the principle that Armortek kits are made to fine tolerances and generally assemble with little adjustment. The things which might prevent a fit are: mating surfaces not clean, slight misalignment, burrs and manufacturing marks on edges. Have a look at the Knowledge Base topic on equipping a Basic Workshop. Some tools which will help include a deburring tool to clean up edges and scrapers. The latter are not widely known but are probably the most useful tools you can use. There are flat scrapers for smoothing uneven surfaces, edge scrapers and scrapers designed to deburr and smooth internal surfaces and bores. All these tools are very cheap to buy and readily available online.

You’ll find with any fit that there is a very narrow margin between an interference fit and a loose fit ie you really don’t have to remove much material to adjust the fit. In many cases it’s misalignment that is causing the problem

I don’t have a PAK 40 so can’t add any specific commments but these don’t seem to common issues.

Finally, on rivets, you can either fit them to function as intended as fasteners, for which you need a river snap and a ball pein hammer or glue them as cosmetic details. There are a few posts on the Forum setting out the best technique. I usually hold the snap in a vice, insert the river into the hole and support the head while rounding and flattening the shaft with the hammer. The shaft will be too long and needs to be cut to the depth of the material to be joined plus one and a half times the diameter of the shaft. Alternatively, cut the rivers, glue them and apply a blob of glue on the reverse to simulate the flattened shaft.

Above all, I hope you get a lot of satisfaction from your model and from developing your skills.

Stephen

[Phil Woollard]

Hi Kevin, sorry to hear your struggling a bit but as your understanding of the parts and how they need to be "fitted" increases you will find it much easyer, I have not had the pleasure of the Pak 40 kit so can't really comment on the sub assemblies your having difficulty with, maybe post some pics of the pieces and I'm sure the guys that have put one of these together will help regards Phil.

[Kevin Williams]

Thanks for responses. I have found your statements to be consistent with mine in that prepping the part and removing burrs and such make the parts fit as intended.


The breech block piece is throwing me. It’s simply too tight to allow the gears to work properly. It only seems to fit one way, but hoping I’m doing something wrong. The pictures in the forum show a tight, square fit and my parts are a little off that. Maybe I had a bad milling?

[Robert E Morey]

Hi Kevin
Welcome to the Armortek forum. As others have mentioned some fitting and filing is necessary on these kits. The Pak40 is my 5th Armortek kit, and I'm finding it especially challenging for fit issues.

I haven't fully assembled everything but I have had the same challenges with:
1) the elevation gearboxes I took a dremel and relieved a lot of the material in close proximity of the gears. This helped them rotate freely.
2) I shortened the treaded length on CQ0187 just a fraction which helps when the brass hex bosses are tightened.
3) I had trouble with CQ0145 and CQ0148. Make sure to deburr where they fit together, and some additional filing was necessary for me to get the breach block to slide freely as well. I have not fitting the opening gears and mechanism on that yet.
4) I had trouble with CQ0145 threading into the barrel, CQ0188. The breach part seizes about half way into the barrel. I have not fully resolved this - the two parts are seized together half assembled, but I will probably machine the diameters of the threads a bit to see if this helps. If not, I will machine the threads off and bond CQ0145 into the barrel.
5) I had trouble with CQ0147 fitting on the barrel. When fitted the holes do not align with CQ0144 mounting block. I will most likely machine a recess in the barrel for the band, and then perhaps make the mounting holes slots (for vertical travel).
6) I have not mounted the rivets yet but I believe they do just glue in.

Use a good grease when first fitting all threaded machined components together as they can easily seize and ruin the threads. I also wash everything thoroughly w hot water and DAWN dish soap to remove the deburring residue on the parts. This is an abrasive dust which if not removed will add additional assembly resistance.

Hopefully this was some help.
Bob

[Armortek]

Hi Kevin,

With regards to your queries, as others above have pointed out, some fettling is needed on the parts.
The machining process leaves burrs on parts that need to be taken off, and in some many cases it helps to take the edges off parts that need to fit together.

With regards to your specific questions:
1. Make sure EJ0146 is deburred and the inside edge is taken off. Same goes for CQ0167. The fit of CQ0167 and EJ0152 should then be good. If not, file the top of CQ0167 slightly. Do not file too much as you do not want slack.
Same will apply to the other gearbox.
2. Make sure to take the edges off the inside of CQ0169 and EJ0153. If that does not solve problem then there are two solution. You can either do as Bob suggested, or do E0153 up to be finger tight and loctite it in place.
3. Rivets can be loctited in. No need to trim the ends.
4. The bottom 2 M2.5s dont have nuts - as you point out, there is no room. These can be loctited into place.
5. CQ0148 and CQ0145 should be a snug fit. If you have trouble joining the parts, then take the edge off both.
6. Yes, CQ0149 should be in place before you tighted CQ0145 and CQ0148
7. The holes should not need to br drilled, but filing through to clear any burr and clearing the edges would do the trick.

Kian