M8 HMC: Step 2 Drive Sprocket

Step 2 in building Tamiya’s M8 Howitzer Motor Carrier is titled “Drive Sprocket”, and deals with exactly that: the assembly of the track drive sprockets. In theory this is an easy step, with the modeller required to assemble two drive sprockets, each consisting of two parts. Unfortunately Tamiya got the track drive sprockets a bit wrong, so although this chapter is still fairly simple, it is not as simple as gluing two parts together.

As I mentioned above, Tamiya got the look of the track drive sprocket wrong: they provide an open sprocket, when in actual fact the M8 HMC was fitted with a solid drive sprocket. Fortunately the Eduard exterior PE set supplies four solid sprockets which can be fitted over both the inner and outer sprockets to make them look the part.

Above are the Tamiya kit instructions relevant to this chapter. The inset shows the Eduard instructions.

As you see from the above instructions, each track drive sprocket consists of only two parts, the inner sprocket (B9) and the outer sprocket (B8). After removing the parts from the sprue and cleaning up any blemishes, my first task was to remove the moulded bolt heads from the outer sprocket. I did this simply using a chisel blade fitted to my hobby knife, but I guess you could also use the grinding head of a rotary tool if you really fancy. Now the kit parts were ready to receive the PE sprockets.

A note to newcomers to photo-etch: photo-etch really can be quite sharp, so you really should practice caution both when removing it from the fret (the frame the PE is attached to) and when handling it.

Aligning the PE parts with the kit parts was simple enough – when dry-fitting it, that is. Why do I say that? Well, if you think about it, when aligning the PE part with the kit part you have to align each point of the PE part with the underlying plastic part – so you have fourteen points to align! Although fairly simple, it can be time consuming. Now try to do it with CA glue applied!

So here is how I handled this problem – and I must confess I only realised this method on a second go at aligning a set of parts. What I did was broke the task down: I only applied CA glue (note that I do not apply it directly from the tube, I put some on a piece of plastic card and then apply with a sharpened match stick or toothpick) to half the plastic part, and then quickly placed and aligned the PE part. Once the glue had set, I gently prised the unglued section of PE up, as seen in the below photo, applied more glue, and then pushed it back into position and clamped the whole part.

Above left you see one of the outer sprockets completed, while other has half the PE bent up for ease of gluing. Above right you see one of the sprockets being clamped.

The whole purpose of the PE parts is to transform the open track drive sprocket into a closed on. However, placing the part does not complete the transformation. When looking at the sprocket, one could see the gaps: one could see the gap in the centre of each sprocket between plastic and PE, as well as the open gears themselves were visible. And so, I decided on the route of least resistance: filling the gaps with Tamiya putty. Once this was done and the putty sanded smooth, the two parts of each track drive sprocket could be glued, and clamped, together.

Above left is one of the drive sprockets being clamped. Above right you see the two completed drive sprockets. Note the use of Tamiya putty visible inside the sprockets and in the centres.

This chapter is not quite over though. You may recall in the first part of this chapter I removed the bolt heads from the outer drive sprockets, and thus these need to be replaced.

Using some (approximately fourteen per sprocket) of the lengths of 0.5mm styrene hex rod which I cut while making the fixes in M8 HMC: Step 1 Errata I replaced each of the bolt heads on the outer sprockets. Each one was glued into place (there is a slight dimple on the PE part denoting the positioning of each bolt) using CA glue. Once all in place, I lightly sanded them all to approximately the same length.

The above left photo shows the front, or outer, of the two completed drive sprockets, while the above right shows the inside.

The next chapter is another short one, and covers the fixing of the drive shafts.

M8 HMC: Step 1 Errata

Following the publication of the last chapter (Step 1) I became aware of two mistakes I naively made during the construction of the road wheel bogeys and the idler wheel units.

A good friend has, since my last post, lent me Tankograd's excellent M8 HMC Technical Manual. While I think they may be a bit too much (in terms of "rivet counting" and information overload) for beginners, I highly recommend these publications to modellers taking their hobby a bit more seriously. While looking through the book I noted that the bogey is mounted to the lower hull with four bolts. The Tamiya instructions, seen in the Step 1 chapter, incorrectly instruct modellers to remove the top two bolts, leaving only the lower two!

So, if you are intending to build this kit: do not remove the top two bolt heads from the bogey front plates! If, however, you naively removed the bolts, here is how I fixed this mistake.

The first thing I did was establish how big the bolts would be. I did this by measuring the remaining bolt heads using my callipers. As I do not own digital callipers, I had to "guestimate" the sub-1mm size. I did this by visually comparing a 0.5mm and 0.8mm plastic rod to the bolt. The 0.5mm was the better match.

Once the bolt head size had been established, I proceeded to cut several 1mm lengths from the aforementioned 0.5mm styrene hex rod. Since I would need bolt heads for later chapters, I proceeded to cut in the region of forty bolt heads. Two bolt heads were then glued into place on each bogey, and then sanded down to a similar height as those moulded to the kit part.

Above you see one of the corrected bogeys.

The next correction of Step 1 is with regards to the location of the PE part on the idler gear housing or unit. You may have noticed that I placed it in a sort of mid-point on the front facing part of the arm. This, per the Eduard instructions I might add, is incorrect! As James McFarlane (and my thanks to James) on Armorama pointed out, and verified in the Tankograd book, the PE part and its accompanying plastic card spacer should be placed at the top of the curved part of the idler gear housing.

The first thing I needed to do was remove the misplaced plastic spacer from the kit part. This was easily done using my hobby knife fitted with a chisel blade. While I could have simply reused the part, I decided to cut two new plastic card circles, and so also removed the PE part from the old spacer.

Next came cutting a new circle. I decided to do this differently to my original method. Perhaps this method I am about to explain is the correct way, but the other method worked just as well.

Using a circle stencil, simply bought from a stationery store, I used a scribing tool to score the circle in the plastic  card. I made the circle slightly bigger than required to allow for waste and mis-cuts.

To cut the circle one simply keeps going around and around, using the scribing tool, until one has cut all the way through the plastic card.

Once the spacer circles had been created, the PE part was glued to the centre of the circle, and the excess plastic sanded smooth until the two parts were aligned. This was then glued to the kit part, and Tamiya filler putty used to fill any remaining gaps. The putty was sanded smooth once cured.

Above are the two corrected idler assemblies.

The next chapter, Step 2, deals with the drive sprocket.

M8 HMC: Idler Wheel Unit Errata Pending

It has been brought to my attention on Armorama that my placement of the PE part on the M8 HMC's Idler Wheel Unit is incorrect. I will be correcting this and an errata will follow shortly.

M8 HMC: Step 1 Construction of Wheels

Step 1 of building Tamiya's M8 Howitzer Motor Carrier is the chapter slightly misnamed "Construction of Wheels". The reason I pedantically say it is misnamed is because firstly the (physical) wheels themselves do not require assembly, and secondly because this chapter actually deals with the assembly of the suspension and the idler wheel units (I actually do not know what the section attached to the idler gear is  called, hence: "unit").

As mentioned above, this step covers building the vehicles four suspension units, each with two road wheels attached, and the two idler wheel units. During this stage I also got my first taste of PE and scratch-building, albeit miniscule, for the kit.

The first thing I do when starting a new chapter, or stage if you prefer, of a modelling project is re-read the instructions relevant to the chapter. Not only the kit instructions though, but also the instructions of any aftermarket (AM) products I will be using to enhance the kit. I normally read ahead through the instructions, ascertaining if there is anything ahead in the build which would make more sense to include at this stage (be it logical sense or from a sub-assembly/painting point of view).

Above are the Tamiya kit instructions relevant to this chapter.

Step 1.1: Suspension

I decided to start this chapter by assembling the  suspension units. As I always do when required to assemble multiple (and identical) units, I identified the six parts required for assembling one of the units and removed them from Sprue B, placing them in a plastic container labelled "Suspension". By placing them in the labelled container I ensure that I can easily find all the parts relevant to the section or sub-assembly, as well as reduce the risk losing them and them attracting dirt and dust. The reason I only remove the parts for one sub-assembly is so that I can do a "dry run" on the assembly, working out any pit-falls that may occur during the assembly, and checking for any seams and casting flaws (which would most likely be persistent on the other, identical parts as well).

Clean up was minimal, and quite normal for virtually any plastic model kit: there were the usual fine casting seam lines. The casting seam lines on the wheels were sanded down using a medium grit sandpaper. The reason I used the medium grit sandpaper was because I wanted to leave a slightly rougher looking finish on the solid rubber road tyre. The rest of the parts were sanded down with a fine grit sandpaper, with heavier seams being reduced first using a hobby knife. While cleaning up the parts, I also took the opportunity to remove the two top bolts on part B17, as instructed by the kit instructions.

Before applying glue to parts it is always a good idea to dry-fit (or test-fit) the parts together to check how, and in which order, they are going to go together when doing the real fit. The kit instructions call for part B10 to be fitted to the rest of the assembly last. I found it was easier to fit the wheels (B10) to B17, and then fit B10. B16 could slide into place over the wheels and into the slot on B17, and seated itself with its arms sitting on the small brackets provided on parts B17 and B10. B7 slotted into place over B16. Placing the completed suspension unit against the lower hull, I also checked the fit against the hull. And thus the suspension sub-assembly was completed, albeit only dry-fitted together.

Having completed the first suspension unit, I clipped all the parts for the remaining units off the sprue and stored them my plastic container. As at this stage the parts and units were all identical (at this point they are neither left or right, front or back) it did not matter that they were all mixed in the tub. Clean-up was as before, as was the dry-fitting of each unit.

Another one of the useful purposes of performing a dry-fit of the sub-assembly is determining to what extent the sub-assembly should be completed, and what needs to be left off for the later painting stage. I decided that painting the road wheels and the inside of the suspension units would be rather difficult it the sub-assembly were completed in its entirety. And thus I determined that it would be best not to glue the wheels and part B10 into place when doing the final assembly.

The final assembly of the suspension was approached in the same manner as the dry-fit. The exception being that the mating surfaces of parts were treated to a dab of Tamiya Extra Thin Cement - the exceptions being those parts I mentioned above which would not be fixed into place just yet.

You will recall that I mentioned reading ahead in the opening paragraphs. When reading ahead, I noted that in Chapter 4 Fixing of Wheels part B2, a D-shaped part which I think is some sort of track return guide or roller, is fitted on top of the suspension unit. I decided it make sense to attach these parts to the suspension units prior to painting, and thus decided to attach them during this chapter. Since the fitting of these parts would effectively define the suspension units as left or right, front or rear, I temporarily placed the suspension units into position and glued the part (B2) into place. I also noted that there was a small gap left on top of the suspension unit. Since I would be leaving the side-skirts off later, this would be visible so filling was required (I do not generally spend too much time cleaning and filling parts that will not be seen). The filling was done with a smear of Tamiya Putty, smoothed when wet with an old hobby knife blade, and later sanded smoother still.

A quick note on the M8 HMC's road wheels: The Tamiya kit is supplied with the open spoke road wheels, however it appears M8 HMCs used these open spoke wheels, the cast wheel, the closed (or welded) spoke wheel, or any combination of these. I have not seen any pictures of the closed spoke wheel used on the M8 HMC, however I am led to believe by those more knowledgeable than me that similar vehicles were using these toward the end of the war so it is fair to assume this was applied to the M8 HMC as well. There are resin replacement kits of the cast wheel available, but as I did not want to spend much more on the kit, I decided not to purchase as set. I believe that as there are a few photos of the open spoke wheel used, I am satisfied that this falls within my reasonably accurate satisfaction level.

The four sub-assemblies (main sub-assembly, two wheels, and part B10) making up each suspension unit.

The four completed suspension units, the four subassemblies dry-fitted together.

Step 1.2: Idler Wheels

Part two of Step 1 Construction of Wheels concerns the assembly of the two idler wheel assemblies. This was also the first stage during this build where I used PE and was required to do some scratch-building (sure it was only cutting plastic from a sheet, but scratch-building nonetheless).

Each idler wheel assembly consisted of three kit parts. With the exception of the idler wheels themselves, the left and right arms were easily differentiated from the other. Once removed from the sprue and cleaned each assembly was dry-fitted. Once again due to wanting to paint the wheels separately I left the units broken down.

This brings us to my first attempt at the kit's PE. The Eduard M8 HMC Exterior PE Kit requires the fitment of a small circular plate (presumably it is part of the idler wheel's suspension arm, perhaps a filler cap for suspension fluid?) to parts B3 and B4, with a 1mm spacer between the kit part and the PE.

By my reckoning there were two ways I could approach making the spacer. Option one was to cut the circle, then glue three parts together. Option two was to glue the PE (using CA glue) to the plastic card and then cut around the PE, creating the circle, and fix this to the kit part. I chose the latter, although in retrospect the former would have been the correct way to approach this task. In actual fact, once the PE was glued to the plastic card I did not cut a circle, but rather a square, and then nibbled away at it until it was cropped in under the PE. A bit rough, but it worked nonetheless. The part, once resembling a circle, was glued to the kit part. Once the glue had dried, the shape slightly further refined using sandpaper. And so my first PE and scratch-building experiences with this kit were complete.

Part B4 with spacer and PE part fixed.

The Eduard M8 HMC Exterior PE Kit provides wedge shaped pieces of PE which should be fitted between the spokes (both sides of the wheel) of the idler gears and effectively make it a solid idler gear. I have noted in photographs that quite a few M8 HMCs operated using the spoked idler wheel. For this reason as well as my decision to use the open road wheels, I decided not to use the PE parts, and to leave the idler wheels as the open version.

The components/sub-assemblies making up the left idler wheel unit.

The two idler wheel units, dry-fitted together.

In the next chapter we will assemble the drive sprockets.

M8 HMC: Preparation

Before we get into the actual building of this kit, I would like to take a further small deviation from the path. I would like to take a few moments to discuss my preparation phase, a phase I consider as important as the build itself, show you a few of the tools I will be using as well as my building environment.

Preparing for the build

As I mentioned above, I consider the preparation phase of a build as import as the build itself. During this time, I normally do a bit more research than I did during the preliminary research phase. I spend a bit more time reading and analysing the reviews and articles I had read earlier, and going through my mind what I am about to do.

One of the first things I do is scan and print (and often enlarge) the instructions provided with the kit. I then use these print-outs and make notes on them. Typically I will note ideas I may have, comments or tips I had read online, or 'danger areas' I need to look out for. When using PE I normally try find the instructions online and will save a copy locally and print them out. Here again I will make notes. What I also do, using a bright textliner pen (or highlighter), is highlight all the pieces on the copied kit instruction sheet which will be replaced or affected by PE. Essentially I create a connection for myself between the two documents.

Above you will see an example of the various instruction sheets with my notes and highlighted parts.

Having now familiarised myself with the instructions, and having a good idea of the flow of this project, the next part of my preparation phase is to check that I have everything I require to build the kit. Now granted I may not have everything at the time and may need to wait for it, so this may delay the build, but better to know up front what is required than to get halfway through and experience a delay. If I know what is required when, I can plan for it.

Part of my checking stage is to actually check the kit contents. Being familiar with the instructions helps, but one can normally tell from the sprues if a part is missing. Fortunately many modern kit manufacturers give you a silhouette type impression of the sprues at the back of the instruction sheets, so you could also use that to check if all the sprues and parts are present and accounted for. At this stage I normally photograph the sprues. This is more for my own record keeping than anything else.

Above are is the contents of the Tamiya M8 HMC kit: Sprue A; Sprue B; Sprue C; Upper and Lower Hulls; Rubber band tracks; and decals.

Above are the two Eduard photo-etch sets: M8 HMC Exterior Set; and M8 HMC Interior Set.

A Few Tools

Every modeller has a few preferred tools which they use. While the No. 11 modelling knife (or similar craft knife) and sandpaper at least are probably considered essential to any modelling project, here are a few of the tools I will be using during this build. I must stress though to beginners, by no means do I consider all these tools essential - these are merely a few of the tools I have collected over years and make my modelling a bit easier.

Clockwise from the top left: Pencil (I constantly take notes in a notebook and on the instructions); sanding stick with medium grit sandpaper (I also have a few other grades of sandpaper, the finer grades are mostly the ones I use); a small spring clamp (for holding parts while the glue dries); pin vice drill and drill bit (very useful if you need to insert pins in figure arms and legs); sprue cutters (the name says it all, but these are from Gamesworkshop and really comfortable to use - but you can get not branded sidecutters for much cheaper); chisel blade (used to chisel details away, cut through thicker resin, and cut PE from the frame); and No 11 hobby knife (used for near everything modelling related - but a craft knife works just as well).

The last few tools, L-R: Reverse-action tweezers (used for handing fine parts); vernier calipers (used to measure things like bolt heads and circumferences of rings and circles - and just because I like measuring things); long nose pliers (again for handling fine parts, but also for bending PE); and lastly but not least underneath is my cutting mat (prevents me from cutting through to my modelling table or board).

Above are two of the glues I will be using, as well as the filler putty. The general purpose glue for all the plastic I will be using is Tamiya's Extra Thin Cement, a liquid poly glue which is applied using a small brush. The Super Glue, or Cynoacrylite (CA) glue, will be used when I need a quick setting glue or need to glue parts of different materials together (like PE to plastic). This can be bought from any supermarket. The putty I use is Tamiya's Basic Type Putty in a squeeze tube. This will be used to fill small gaps and holes.

My Building Environment

Now you might be wondering why I am letting you look in on my building environment. The purpose of this is to demonstrate that you do not need a special room to build models in - yes, it certainly is nice, and I do wish I had my own room, but it is not a necessity. I currently live in a smallish apartment with my wife, and so space is somewhat limited. All my modelling takes place in our lounge. And it being our lounge means that my area need to be neat, and the ability for either one of us to move my stuff quickly, effortlessly and safely if we have guests. And with that in mind, I bought a Citadel work tray a few years ago (when we were in our first apartment).

This is my nook. The desktop was previously installed in corner, and during the day with the blinds raised has a great view of the local botanical gardens. My modelling tray fits on it easily, and I have space to either side while I work. You will note to the left of the table my instructions on a book stand (normally for recipe books) with the PE instructions underneath and the area of current focus visible. I have a short fluorescent desktop light for working at night. The notebook speaks for itself. The kit and toolbox and stored neatly on the floor in the corner. To my left is the TV, so that I can keep my wife company while she watches TV or plays her Nintendo Wii.

The last bit of my environment, although perhaps this could be seen as a tool, are the plastic tubs I use. These tubs originally held salad from the local supermarket, but now make great containers for holding model bits. When I build the various sub-assemblies, I keep the parts and built sub-assemblies in their own tub (so I may have a few different tubs) with a bit of masking tap containing the name of the sub-assembly across the lid.

Now that we have this background, we are ready to start the build.

Building Tamiya's M8 Howitzer Motor Carriage

I have always liked the stubby look of the M8 Howitzer Motor Carriage (HMC). Well ever since a friend sent me the 1980's era Tamiya 1/35 scale kit of the vehicle. I must confess prior to that, I suppose mostly to my extremely limited vehicle knowledge, I had never heard of this self-propelled artillery piece. Even more so since my WWII focus is normally that of Germany.

Looking for an easy Christmas holiday build, I decided to pull this kit out and give it a go. And so, I started the build with what I call the 'project initiation phase'. This is a pre-build period during which I look for reviews, blogs and build articles of the kit, and even just photos of the completed model. I do not restrict myself to only the aforementioned articles about the kit, but also look for similar articles about other kits of the vehicle, and maybe even different variants of the vehicle. During this phase I also conduct some minor research on the real vehicle. At the end of this phase I decide, based on the amount of effort required to put the kit together to a level which I find acceptable (I do not consider myself a 'rivet counter', unless we are talking figures, so I am generally not bothered if a hull is 1mm out or the kit not 100% accurate, but I do like the kit to look good and be reasonably accurate), and if I still want to go ahead and build the kit. I quite obviously decided to go ahead with this project.

During my preliminary research phase I came across a great article about building the kit on PMMS by Terry Ashley. This article would later become one of my main references in building the kit. In reading Terry's article I noted that Eduard had released a photo-etch (PE) set for this kit and also that the tracks were particularly dreadful, but that AFV Club had released an excellent track set which would work for the kit.

Now something I also like to do with each model is to set some personal goals. These goals might be something small like trying a new painting technique or something large, such as in this case. It has been a few years since I tried using PE, so I was really keen to try it again. Unfortunately Eduard has discontinued the PE set Terry used during his build. They have, however, released two new kits to replace it. An exterior and an interior kit.  What the heck I though, in for a penny, in for a pound. And so promptly ordered both kits from LuckyModel. Something else I wanted to try was individual link tracks, and so was pleased to find the AFV Club track set at one of my local hobby stores.

Unfortunately the PE sets did not arrive until the first week of January, a few days prior to my vacation ending and thus the delay in the build actually beginning. So much for a Christmas holiday build! LOL! That said, my thanks to the staff at LuckyModel for kindly splitting my order and sending the PE sets ahead of the other items on the order.

 

Above are the kits to be used in this build: Tamiya 35110 1/35 M8 Howitzer Motor Carriage; AFV Club T16 Track; Eduard 35509 M8 HMC Exterior Kit; Eduard 35530 M8 HMC Interior Kit.

My approach to this build

Perhaps a quick word on my approach to this build is in order. While I have been modelling for years, I have not built an AFV in about 3 years. I do by no means consider myself an accomplished modeller, especially not an accomplished AFV modeller. And so this step-by-step (SBS) article will be written very much from a beginner point of view for beginners. I will mostly be following the kit instructions, deviating from them occasionally where my (sometimes misguided) logic tells me otherwise. The chapters of this build will follow those of the kit instruction sheet, so some instalments may be larger than others.

I should also add that I assemble models in sub-assemblies prior to painting. I find this method works best for me. 

I unashamedly confess that I do not now what many of the technical terms are for parts of the vehicle, and apologise in advance if I do not call something by the correct term.

The techniques I use here are techniques I have read both online on various modelling websites and in various modelling magazines, as well as techniques shared by good friends. I use these not necessarily because they are the best or right way to do something, but rather because they are the ways that I find easiest given my level of experience and yield results which I find acceptable.

The next chapter of this SBS will detail some of the tools I will be using.