Churchill Mk3 number 67

[David Skeldon]

Hi,

I reshaped the Armortek bracket and added a steel hook, not quite like the original on but seems to pull my universal carrier ok .



David

[Gary Richardson]

Hi all

I have made progress on the tow hook assembly, I decided to make it out of a single piece of brass. I believe it is Naval brass as it is extremely hard and only very thin layers at a time could be removed with the mill.
As you can see from the photos it starts out as a solid piece of round rod, and takes a lot of milling to get it to the basic shape. I intend to try and make the mechanism work that engages to keep the hook closed. I have had to simplify some of the external extras slightly as my milling skills are still being stretched.
This morning I drove to Bovington and checked all the tow hooks of this type ,three Churchills and the Comet. Luckily on the MK4 Churchill the top cover has been damaged and is open to reveal the innards of the tow hook main body.
There are four rollers on an L shaped assembly inside on a rod that passes through the main body, this rod is operated by a lever on the side of the main body. The lever is operated by a cable protected by a steel tube. Although I could not see the lower rear part of the hook where the rollers engage I think I will be able to reproduce how it works.
I decided to use M3 studs in the mounting block and attach the tow hook with nuts and washers as per full size, I have not shaped the two flanges with the holes yet and in reality the studs are much closer together at the lower half of the flange. See photo in my last post and the next paragraph.
I also noticed the hook assembly is not mounted on a solid block but rather an triangular steel shape attached by four bolts to the bottom of the upper rear plate and welded to the hull base right at the corner, so it only attached at the top and bottom with quite a large gap between it and the hull. I will have to think if this is something I can replicate on my AVRE.
While I was looking at the Mk3 AVRE a man and his grandson were also looking at it, we started talking about the Churchill and it turned out his father was in one during the war. The tank took a direct hit and his father was the only member of the crew to survive. He wasn't sure what type of Churchill his father was in so I explained the differences between the AVRE, Mk3, Mk4 and the Mk7. Hopefully I did it justice as he said he was going to make some enquiries and try and find out more about the tank his father was in.

Regards
Gary

A very tough chunk of brass

Getting the base and rear surfaces flat

Starting to take shape

Drilling the mounting holes

Progress so far, a lot more internal milling is required.

[Vince Cutajar]

Nice.

Vince

[Derek Attree]

Hi Gary
I love machining brass

Looking good

Regards

Derek

[Gary Richardson]

Good afternoon

The tow hook assembly is coming along slowly. I think I have devised a way if locking the hook in place whilst towing. It will be lever operated and I have tried to keep the external features similar to the full size while retaining the original mounting block. A bit of poetic license has been used and the lever had to be repositioned due to the top fixing stud and nut.
It will work by lowering a flat surface stop against the rear of the hook which will have a 90 degree angle cut into it. At present I am experimenting using a M3 bolt as the stop but intent to mill two of the sides to leave a bar across the threaded section. This will make it easier to raise and lower it against the hook notch. I used an brass M2.5 axle collet from my aircraft surplus . I tapped an extra M3 hole for the bolt and together with two grub screws this will secure it on a M2.5 brass rod passing through the tow hook main body. I have added the relevant notches and holes so I can operate the lever via a cable through some pipe as per full size. If I add a small spring to the cable at the leaver this will also help keep the tow hook closed. The hook will be remade out of 6mm wide steel once I have sourced some offcuts from somewhere.
Hopefully the photos will show what I am trying to achieve.

Regards
Gary

20 hours taken so far

I think this mechanism will work

[Gary Richardson]

Good morning

I made a bit more progress on the tow hook assembly yesterday. The mechanics work ok after a lot of fettling. The tow hook has been made from steel and still needs to be filed to the final shape. The hook had a 90 degree notch milled from the rear section which the M3 reshaped bolt sits in to stop the hook opening. The lever works this stop and will be cable operated either manually or from a small servo inside the rear hull.
While the assembly is not a replica of the full size I think it looks ok. It functions as per the full size which is what I was aiming for bearing in mind the size of the trailer I intend to tow.
I am hoping to get it completed today as it has taken far longer than I anticipated due to all the tiny milling adjustments I had to make to get if to work.
Next job will be to start assembling the tracks while I wait for the modules to arrive. I am still not sure about having to use the knurled ended track pins as I imagine they will be difficult to remove if the track needs separating to replace links later on. I like Adrian's idea to have clean pins with a groove in the middle and pointed grub screws so they can be removed easily. I will start looking into this once the tow hook is finished.
If any of the other Churchills builders has ideas regarding the track pins feel free to jump in

Regards
Gary

Almost complete

Hook stays closed once stop has engaged

[Gary Richardson]

Hi all

Well I have finally finished the hook assembly. The hook stop has been silver soldered to the collet to avoid it moving now the correct adjustment has been made. I have added a return spring to the lever which also means when the hook is in the open position it also stays there with the stop holding it open from above. A win win situation. The hook can then be gently pushed closed and the stop snaps into the locked position.
I made a brass cover to keep the locking mechanism clean, it's a bit larger than on the original but again it serves the purpose and could easily be taken for a field mod if the original was lost
I just need to get it primed and paint then install it on the tank. I will sort out the cable pipes later once I have the modules and can start on the cable loom.

Regards
Gary

Ready for a clean up and priming

cover is held in place by a single M2 bolt

[Gary Richardson]

Good afternoon

The tow hook assemble is now on the tank. I am very happy with the result, although with hind sight, there are a couple of things I would have done differently such as simplifying the way I used the mill to cut out the central recess. Still, it is all part of learning new skills so time well spent.

Regards
Gary

[Gary Richardson]

Hi all

Having a quiet day so just adding welds to the front of the hull. I have looked a five different Churchills and they all have differences in how welds were applied. The large welds on the Tank Museums Churchill Mk3 AVRE are more likely wading plug material, at least that's what one of the curators told me. They do seem very large to be welds. One Churchill shown in a walk around series of photos on line doesn't appear to have any welds at the front except for the bullet deflectors.
I have gone for what I feel is correct and is shown on a Mk4 at the museum. I suspect the AVRE's had welds applied after the refit and before D-day.

Regards
Gary

A bit more weld detail added

[Gary Richardson]

Hi all

Things have been a bit quiet on the Churchill front as I have been cleaning and fettling parts that can be painted such as the plates that protect the bogies. I am at the stage where I will start adding the various paint finishes to the wheels and bogies, lower hull and sprockets. As when I painted the Tiger, I will use a mix of acrylic, enamel and Abteilung 52 oil paints. A lot of the well known washes are enamel paints which can be used over acrylic paints but you cannot then add acrylic over the wash so some planning is required. I really like using the oils and will do the rendering using the spot method as per the Tiger. A barrier of Citadel matt lacquer will be applied prior to using the oils making any mistakes easy to rectify. I am not sure how effective it will be on the SCC15 top coat so I will experiment using a mix of lighter and darker colour from the spectrum of that paint.
I have started assembling the tracks but still have concerns about taking the tracks apart in the field. Having assembled sections of five track links at a time I have found adjustments to the track link holes was required to get the pins through in about fifty percent of the links. The knurled end of the pins can be very tight requiring pressing in a vice to get them home which obviously makes it difficult to remove them. Some pins were quite loose but swapping the pins to other links that were a bit tighter solved that problem. I therefore decided to order some 5mm stainless steel rod and pointed M4 x 4mm stainless steel grub screws and will use Adrian's method of quick release pins that he posted on the forum.
Thankyou Adrian for showing the solution.
I will add a quick release pin every five links plus a couple between three links to allow easy track length adjustment while the tracks bed in.
One bonus of tinkering with the pins and link holes is if you leave the pins on the tight side through the holes you get a loud squeaking noise as they move. It sounds just like the real thing, I will try and get at least six of the links and pins to do this while making sure the others are all freely moving.

Regards
Gary

Sets of five link to enable quick release pins to be used

[Gary Richardson]

Hi all

So here I am doing yet another mod/addition. This time it is the spare track link brackets at the rear of the panniers. I am using a photo I took of the MK4 at the Tank Museum as the basis for the top and bottom brackets. Again this mod turned out to be a bit fiddly, mainly getting the brass to curve and bend at the correct places. The top bracket still needs some adjustment as the loop is too long, I am sure there must be a simple tool I could make to help bend the brass and will look into it for future use.
For the bottom bracket I milled some 12mm brass angle until I got the correct thickness and side measurements then silver soldered a brass tube along the edge. The top of the tube was milled away and then the centre was cut out, the end plates were then soldered in place. A short length of 5mm stainless steel rod goes through the track holes and rests in the tube section.
The top bracket is self explanatory as shown in the photos. Both brackets are held in place with M2.5 bolts after I had drilled and tapped the holes in the rear plate.

Regards
Gary

Photo courtesy of the Tank Museum.

Starting the top bracket.

Tapping the M2.5 holes

Shaping the top bracket

This bracket took a lot of time to get right.

Trial fit to spot the drill points

Top bracket needs the loop adjusting so it is shorter.

[Gary Richardson]

Hi all

The spare track link brackets have been adjusted, painted and installed. I then started on the modified track pins. They have been drilled on the lathe and hand tapped with M3 threads 5mm deep at one end making them easy to remove with a threaded tool I will make later. Three of the pins had the tap break inside during the process so will have to be remade. The quality of the stainless steel 316 rod seems to be the problem with one of the three sections of rod I ordered having a dark grey impurity in it that looks like tiny gains of grit. I will order some more rod from a different supplier and some more M3 taps.
It looks like I will have seventeen removable pins per track, roughly one every five links with a four link section having more pins to allow easy track length adjustment during bedding in.

Regards
Gary

Phone was too close which has distorted the bottom bracket. It is level across the width.

Track link is held quite firmly with very little slack

Just over half the pins I will be making.

First use of my new lathe.

Playing lucky dip with the pins. Broke three taps in the process.

[Sean-Armortek]

Hi Gary.
Two things so you don't break taps, try starting the thread tapping whilst still in the lathe, you can use you chuck on the tailstock to true the tap to the hole. Some taps have dimples on the back so the tailstock can centre it as well.
Also that's a spiral point tap, meant for through holes, not blind. Try looking for a spiral flute as it ejects the swarf up and out of the hole, your one pushes the swarf down into the hole. Or better yet, drill to 2.8mm and use a form tap.

Edit: When tapping stainless, you should drill 0.1mm larger than normal if you are using a cut tap.

[Vince Cutajar]

All excellent tips by Sean.
I have used 316 a lot and did not find many problems using it. 303 machines even better. Avoid 304 like the plague.

Vince

[Sean-Armortek]

All excellent tips by Sean.
I have used 316 a lot and did not find many problems using it. 303 machines even better. Avoid 304 like the plague.

Vince

Interesting you say that as I see nothing wrong with 304 and actually prefer working with it over 303, which can be a bit gummy as far as stainless goes. Main trick to machining any stainless is simply do the opposite of what you assume would improve the cut. IE, in most cases, it's better to run with no coolant and increasing the feed rate, only ever introducing coolant to finish passes and drilling/boring operations.

If you have worked with 718 inconel, then stainless is a breeze