Seiko 7A38 - by the numbers



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Forum Home > Parts Info, Tech Tips and Tinkering > 7Axx Prototype Movement Holder

Site Owner
Posts: 13287

We've already mentioned this in a couple of different threads in the 'Tinkering' section, and two members have expressed interest. ;)

It's certainly something I've thought about making myself before. 

But before I go any further, let me copy and paste those posts over into this thread, by means of an introduction. So bear with me. :P

February 29, 2012 at 11:58 AM Flag Quote & Reply

Site Owner
Posts: 13287

Originally posted by me, in a response to a post by Chris on 21-02-2012:

That isn't really a 'movement holder' as such - just a watchmaker's vice. I've got a similar-looking one myself - without the base-plate.

The quality is pretty abysmal really, and I mostly use mine for holding a watch case when I'm dealing with a tight case-back.

This is a proper Seiko movement holder, for Caliber 6138:

That photo came from a short thread on SCWF:

There's a few more examples in this other thread:

I've been trying to get hold of original Seiko one for 7Axx's - if such a thing actually exists. 

But I may look into getting some made up by my local engineering shop (in hard nylon) if there's sufficient interest. ;)

February 29, 2012 at 12:05 PM Flag Quote & Reply

Site Owner
Posts: 13287

Trying to strip down a 7Axx movement in one of those cheap, ex-eBay watchmaker's vices with the nylon pegs is not ideal, because they don't locate the movement positively. As I've written before, this type of vice are really only suitable for holding watch cases.

Not only that, but the pegs can get in the way, when you get down to main base-plate level. This is someone else's borrowed photo:

Note how the nylon pegs are obsuring the very corners where the crown stem and pusher actuators are located. :mad:


There is another type of watchmaker's vice which is better suited for use as a movement holder, with a radius machined in the jaws.

Here's a small* cheap (and presumably low quality) example currently on eBay for £2.99:

*By the way, I asked a question of the seller, and he replied that the maximum diameter movement that vice will accept is only 25mm.

This appears to be a larger, better quality version of the same thing being used by John 'TheTigerUK' Bentley in a thread on SCWF:

This was a 7A28 movement where John was demonstrating how he sorted out rusty pusher actuator levers. Superb photos, eh ? ;)

Here's a not-so-wonderful photo I posted in athread on RLT a while back, showing a partial strip-down on a 7A38-7270:

On this occasion, because it was a Q&D clean-up - a similar exercise, but with less extreme rusting, I did it in situ - in the watch case.

I'm borrowing Simon's photo here, from his 7T34-6A00 rebuild thread - I'm sure he won't mind me using it 'for illustration purposes'. ;)

Simon was working on the top side of the watch - replacing the dial and re-setting hands on his 7T34, which prompted my comment:

February 29, 2012 at 12:14 PM Flag Quote & Reply

Site Owner
Posts: 13287

Originally posted by me, yesterday, 28-02-2012, in Simon's 'Putting it back together (almost)' thread:

I take it (from looking at one of the photos in your 7T34 thread) you may* have bought a set of Cousins plastic 'cups' p/n M0984 ?

Did you look at the 'specific' movement holders underneath ?

Hopefully I'll be able to catch up with the engineer at work who can operate the plastic moulding prototyping machine, this week. ;)

They call it a 3D printer (it's huge). Effectively you feed in your CAD drawing and it squirts molten plastic to form the desired object.


*Edit: Or are you using a couple of dies from your crystal press as a support ? :/

February 29, 2012 at 1:05 PM Flag Quote & Reply

Site Owner
Posts: 13287

Posted in Simon's same thread earlier today - original post now deleted and moved here:

This is what we've got a work - a Dimension BST 3D printer:

Should be able to knock something up in the next couple of days. :)

See also:

There's lots of other clever stuff on YouTube - so cobbling up a prototype 7Axx movement holder should be a cinch. 

February 29, 2012 at 1:18 PM Flag Quote & Reply

Site Owner
Posts: 13287

 So, early this morning, I was taking various measurements off a gash 7A38 movement which had been soaking in WD40 for months.

When I got to work I got my sketch pad out (literally) and sketched out the first prototype .... typical 'back-of-a-fag-packet' stuff. :D

Here's a first pass done using Google 'SketchUp', before it was converted to a proper CAD file which the 3D printer could read:

O.K. Let me try to run you through my logic in designing it the way I have, first ....

I'm trying to design a generic movement holder which will work for all the conventional 7Axx movements - 7A28, 7A34, 7A36, 7A38 and 7A48. I'm not going to attempt to cater for the 7A07 and 7A54, because apart from their very limited appeal, they also have different pusher lever actuator mechanisms and diameter main plates. The most popular movements are the 7A28 and 7A38, but because the 7A28 has no day / date complication, it's a millimetre thinner - approx. 4.0mm, as opposed to 5.0mm - so there's a first consideration.

I'm also trying to design something which can be used to hold / support a movement either dial face upwards (say for fitting hands) or back-plate upwards, as in doing a strip-down - WITH or WITHOUT the dial fitted. So there will be some compromises in dimensions.

Let me run you through the nominal dimensions of the first prototype, starting at the bottom, working upwards ....

The base is 50.0mm square and 15.0mm deep. The logic behind having a square base is that you can hold it between your fingers comfortably - or alternatively you could mount it in a vice, or even drill the corners and screw it to a work-top. Currently it is solid, but I am considering (in Rev. 2) having four triangular 'wells' milled into the corners, into which you could drop sorry, I meant 'place' :P say back-plate retaining screws and other small parts, as you remove them.

The cylindrical main body is 40.0mm in diameter and 25.0mm tall. They just seemed nice round numbers. Maybe it doesn't need to be quite so tall (overall that makes it 40.0mm high). I chose 40.0mm as a 'median'. 7A38 cases vary in diameter from 37.0mm to 43.0mm - but as we're dealing with the movement out of the case, it becomes irrelevant. Particularly, as if they go into low-volume production, each movement holder will be supplied with a full-length uncut Seiko p/n 0354728 crown stem - of more anon.

The machined recesses in the top is where it starts to get interesting. A 7A38 movement is nominally 31.1mm (according to the Orient J3920 spec' sheet), with a dropped diameter (of the lower part) of 29.0mm. Well, the one I measured was 31.2mm, and if you make allowances for the bulges underneath the 'pips' on the green plastic '710' insulator spacer - see below, you need to go slightly bigger !

Initially, on the prototype I've gone for an inside diameter of 31.5mm - on the basis that you want to be able to get the movement out !

The first step is 4.0mm deep (rather than 5.0mm), so that a 7A28, or a 7A38 with the day-date complication removed, just sits flush.

The next recess is 28.0mm diameter, and I'm trusting that will clear all batons and lume pips on any 7Axx dial, and sweep hands.

It is currently also 4.0mm deep to clear any hands in situ - doesn't really need to be quite so deep .... but better safe than sorry.

That lower well can be filled with a removeable 28.0mm x 4.00 disk, suitably machined to match the back-plate / screw heads, etc.

The 4 cut-out slots are arranged around the dial at 120°, 60°, 120°, 60° intervals, to align with the crown stem and pusher lever actuators. They are all 1.0mm wide by 4.0mm deep. Originally, I was going to make the three 'pusher access slots' 3mm wide, but thinking about where the crown stem (which will be used to locate the movement) would end up when you flip it over .... Right ! :roll:

Please give me your inputs / thoughts on the chosen design / dimensions by the weekend. Thanks in advance. ;)

February 29, 2012 at 1:27 PM Flag Quote & Reply

Site Owner
Posts: 13287

Ooops. Nearly forgot to mention - the first prototype model was finished this afternoon at around 4:00pm ....

With thanks to Mervyn (at work) for all his help, and efforts on my behalf, so far. 

February 29, 2012 at 2:51 PM Flag Quote & Reply

7ARCool ©
Posts: 168

Awesme work Paul :D

Crazy Tech being able to print 3D objects ! 8)

February 29, 2012 at 6:20 PM Flag Quote & Reply

Posts: 32

That's looking great Paul.  Are you a commercial designer?  Your thought process in the design seemed so clear.


February 29, 2012 at 7:53 PM Flag Quote & Reply

Site Owner
Posts: 13287

No, John - just a 'Jack of All trades (and Master of None)' .... making good use of the facilities at my place of work. :D

Subtitled: Close (too close in fact) - but no cigar (yet). 

I picked up the first prototype at work this morning. It didn't turn out to be quite the working model I was hoping for. :(

Certainly not what you'd call an unmitigated failure, by any means. ;)

First of all, in terms of overall dimensions, I think I've pretty much got it right.

If feels comfortable between forefinger and thumb, though I'm not sure if it really needs to be 40mm high overall:

In the photo above you can see how the 3D printer constructs the model. Basically, it extrudes a thead of molten plastic (at 280°C), building up the model layer by layer. I think the engineer running the machine said the thread was 0.2mm, but it looks thicker in some places. He did warn me (partly because of the 1.0mm 'access slots' I was forming in the top layer), that there might be some risk of distortion. Yesterday morning, I had actually measured the widest part of the movement - the '710' green plastic spacer at 31.21mm. My gut feel was to go for an ID of 31.25. Then I thought, No - let's round it to 31.3mm. In fact, what we finally decided to go with was 31.5mm ! I was thinking to myself afterwards, this isn't going to be any good - the movement is going to be flopping all over the place. 0.29mm is a lot of play in horological terms. I took a gash (badly battery acid damaged, minus dial and hands) 7A38 movement into work with me this morning - itching to try it out. Absolutely NO WAY would it even begin to fit, and I suspect if I'd tried to force it in any depth, I never would have got it back out again.

When I got home this afternoon, I tried out a couple more movement parts, separately, starting with a partly stripped rusty one:

Slightly different view without my fingers. In both of these shots, the movement base-plate was barely pushed into the holder:

The only reason I managed to get the slightly larger diameter '710' plastic spacer / insulator to fit, was partly because of its inherent 'give' when not assembled into the movement, but also because this one was actually broken. So a bit of a pointless exercise really. :roll:


Here, I literally forced the 7A38 Day / Date spacer (I think Seiko call it a 'Dial Sheet' in the parts list) a bit deeper into the holder. 

Getting there, I think. :)

March 1, 2012 at 11:19 AM Flag Quote & Reply

Sir Alan
Posts: 458

It's coming along nicely Paul, and is clearly going to work.

Is there any 'give' in the material, or does it behave like a rigid plastic?

And, ..... is there any choice on colour?

March 1, 2012 at 12:29 PM Flag Quote & Reply

Site Owner
Posts: 13287

It depends whether I carry on 'playing with models' or decide to 'bite the bullet', and go and visit my local engineering shop, Simon.


There certainly is 'give' in this extruded prototype - that's how I managed to force the dial sheet spacer in to quite a depth. 

But there won't be ANY give in the production version. It will be turned / milled in hard engineering nylon - Delrin, probably ... 

The same material the dies in your crystal press are made out of. That's why the dimensions need to be exactly spot on.

I know from experience (from my slot racing days) that this kind of nylon can be dyed with vegetable dies (Dylon, etc.). 

Mervyn did suggest that it would look really nice done in aluminim, then anodized metallic blue. I'm thinking about cost. ;)

March 1, 2012 at 1:12 PM Flag Quote & Reply

Site Owner
Posts: 13287

In the meantime, I've been casting around for more ideas - never averse to plagiarism. ;)

Check out this selection of better quality (some better described than on Cousins website) movement holders on Otto Frei's website:


In case you don't think in 'Lignes' - and I certainly don't .... 31.5mm Ø is as close to 14 Lignes as makes no difference.


Note also: A*F movement holder # 185.138 halfway down the page - for ETA Cal. 251.2xx - a fairly popular quartz chrono' movement used in many TAG and Tissot models. The more I think about it, I'm sure Seiko must have a ready made holder specifically designed for the 7Axx series movements. I'm going to ask the question, before I expend too much effort 're-inventing the wheel'.

March 1, 2012 at 1:21 PM Flag Quote & Reply

Site Owner
Posts: 13287

I haven't completely forgotten about this, by the way. :/

An attempt at a second 3D prototype, with fractionally different internal dimensions failed - ending in a warped pile of plastic sprue. :(

So the next logical stage would be to go to the local machine shop, and get them to run me up a sample. Having it milled in one piece (as the prototype was 'moulded') would be prohibitively expensive. Far better to get the cylinder turned (in nylon), and then screw it to a base in possibly another material - maybe aluminium or wood. But now I'm thinking about possibly forgoing the base altogether.

Have a look at these couple of recent threads on SCWF:,30370.html Seiko OEM movement holder details required (please).,30099.html  FS: Seiko movement holders $25 plus postage SOLD

Note that some of them appear to be double-ended, with different cut-outs. Now, there's food for thought. 

April 1, 2012 at 1:51 AM Flag Quote & Reply

Site Owner
Posts: 13287

The first step is 4.0mm deep (rather than 5.0mm), so that a 7A28, or a 7A38 with the day-date complication removed, just sits flush.

The next recess is 28.0mm diameter, and I'm trusting that will clear all batons and lume pips on any 7Axx dial, and sweep hands.

It is currently also 4.0mm deep to clear any hands in situ - doesn't really need to be quite so deep .... but better safe than sorry.

That lower well can be filled with a removeable 28.0mm x 4.00 disk, suitably machined to match the back-plate / screw heads, etc.

What I'm thinking now, instead, is one end for performing back-plate downwards movement strips; the other for doing work on the top end - day / date complications, dial fitting and hand setting. Wouldn't that make for a more useful 'all-in-one' movement holder ? :)

April 1, 2012 at 4:19 AM Flag Quote & Reply

Sir Alan
Posts: 458

I guess you're saving material with the 2-in-1, but I'm not sure you'd save cost (since the effort is in the precision machining?)

And, you could only work on one activity at a time.

If I had a vote, I'd say keep them separate.

April 1, 2012 at 4:31 AM Flag Quote & Reply

Site Owner
Posts: 13287

Some of you may have noticed, from a photo I posted elsewhere on the forum, that there exists a Mark 2 prototype movement holder.

Except in that Q&D photo I rattled off this afternoon (for illustration purposes) I quickly popped the Kamatz V906 movement into it ....

without thinking to align the other three 60° slots in the 'barrel' with the pusher actuator levers (as it was intended to be used). 

The most obvious difference is that this one has the four little receptacles moulded in the base to 'drop' your back-plate screws into.

However, it is actually quite different from the Mark 1 prototype - and it works ! :D

I'd twisted Mervyn's arm (the helpful mech. engineer at work) to knock me up a third prototype on the 3D printer, back in early May.

Only Merv being Merv decided he was going to do it differently. He decided, despite my protests, that he was going to make it taller ....

Much taller ! :o .... and that rather than trying to achieve a precision fit, he was also going to make the 4 slots much deeper, on the basis that the inherent springiness of the material would grip the movement. It did - too bl**dy tightly. Unfortunately, Mervyn hadn't allowed enough for 'shrinkage' in the moulding process. I could just about force a (completely gash) movement into it, but I had to literally lever away at it with screwdrivers to get it back out again. Not ideal. So eventually, I persuaded Mervyn to chuck it up in his lathe, reduce the height to something more sensible, and to machine out the top step again to 31.25mm - exactly. Now it very gently grips the pips on the perimeter of the 710 spacer - so perfectly, with just a hint of spring loading, due to the four extended slots.

You don't actually need to locate the movement with a crown stem, to stop it turning as you undo or tighten the backplate screws. :)

This second photo shows the movement correctly oriented, with the other 3 slots properly lined up with the pusher actuator levers.

Of course, in a production version it would probably make more sense to have 6 slots moulded every 60°, to stop any 'misplacement'.

July 8, 2012 at 4:20 PM Flag Quote & Reply

Site Owner
Posts: 13287

A couple of quick updates on this. The project isn't forgotten, by any means - just that I've had other distracting priorities (at work). :(

Mervyn, the helpful engineer at work was made redundant in the middle of June. The mechanical engineering lab is totally dismantled.

The 3D printer, on which the first two prototypes were produced, was donated free to the Science Museum annexe at Wroughton. :roll:

But every day, on my drive to work I pass this place: 

Yesterday, I called in and spent about an hour chatting with one of the directors, John Hemsworth. He's also a bit of a watch fan. :)

Whereas the costs involved with tooling and injection moulding any such movement holder are completely out of the question ....

They have an incredible array of machinery, including 4 CNC milling machines - and offer a few other interesting services besides.

We've talked in principle about CNC machining a next prototype from solid in black Delrin. The costs involved aren't too prohibitive.

August 1, 2012 at 8:48 AM Flag Quote & Reply

Rob Benham
Posts: 277

Just trying to read in during the early hours of the morning.   This thread is of interest to me as I've spent some time in the garage sorting though white PVC plumbing in the hope of finding the basis of something like the above.  I did, but there it ended.  Again, I feel the frustration of being away from my old workshop.  A Myford lathe would have turned out the inner diameter of a short coupling which was almost the exact size.  With not too much supportive lip to stay clear of the dial, I'm left with a good 2mm of this strong material. Indeed, if the supports were 5 or so horizontal plastic pegs, one could vary the drop into the tube and indeed, be sure the watch didn't drop in.  Such pegs could be arranged to be away from all of the hands.

Simply plugging it into hole in another cheap cutting board would provide the base.  In fact, as far as fitting it to a base goes, my collection of irrigation bits are probably nearly as extensive as your watches, and I could fit the new holder to almost anythng.  Why, I could even arrange for a flow of hot air or fluid through it.  :D

Serioulsy though, with a very sharp cutting tool, this stuff mills very cleanly.  Cost of part - 25cents.

Oh, BTW, I've just been recalling a beautiful little lathe I'd seen here in about 1976.  It was too big to be described as a watchmaker's lathe, but could be adapted.  Only 15" long and very heavily made - and enammeled? in a light cream.  Used to see a few of those back then, but haven't seen one for years.   Does any forum member have anything like that?

January 10, 2014 at 3:25 AM Flag Quote & Reply

Posts: 508

Paul, I hope you are making progress in this project, since I am seriously interested in offering the right money for a couple of these holders, or maybe 3. All the movement holders I have (3 in total) are of the adjustable type, are cheap made and are of really no help...

Let me know when you are ready to manufacture a batch, I am seriously interested in this.


My personal Blog:

January 24, 2014 at 9:19 AM Flag Quote & Reply

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