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Machining Castings

Manorfarmdenton

Registered
Whilst I have done a lot of full-sized machining of parts for tractors and engines, I'm relatively inexperienced with model-sized bits and pieces. However, I have recently started on machining a set of castings for a 1/4 scale Red Wing open crank engine supplied by Engineers Emporium here in the UK. The drawings that came with the kit are by P.M.Research Inc.

My problem is that there is insufficient metal in some of the castings to achieve the dimensions shown in the drawings. e.g. flywheel diameter and width of face, length of cylinder bore, etc. I realise these dimensions are not necessarily critical (e.g. the piston misses the head by around .5" at tdc!) but does this not defeat the whole object of working to drawings? Or am I being too fussy?

I have spoken to the suppliers, who said it wasn't critical but they are happy to replace the flywheel castings anyway, as it appears that at least one of mine was faulty. There was a radial displacement of the two halves of the mould - which would not have mattered if the foundry had been slightly more generous with metal in the first place!

I am interested to hear the views of others more experienced than myself, and particularly anyone who knows the Red Wing model.
John Fearnley.
 

gbritnell

Registered
Re: Machining castings.

Hi John,
I'm not familiar with the Red Wing castings but have machined my fair share of other kit castings. I would say that there is a big difference between suppliers. Some are concerned about the product they sell and others couldn't be bothered. I have been machining castings for several Galloway kits. The original castings in some cases had minimal stock while others had too much. The new company that's marketing them is trying to rectify all of the problems with the drawings and the castings. I suspect that the Red Wing castings were bought by PM Research and it's possible they suffer from some of the same problems as the Galloway castings. I was a metal patternmaker in the auto industry for 40 years. The idea of making a casting was to reduce the amount of metal used while still providing the proper amount of stock for the machined areas.
As far as I'm concerned if a drawing says that a part should be 5 inches long after machining and the casting is already 4.98 then the patterns should be corrected.
The best castings I've ever worked with were Stuart castings. There was alway enough stock to clean up and the quality was excellent.
gbritnell
 

chrsbrbnk

Registered
Re: Machining castings.

A lot of the casting kits I have gotten have castings that are short of material to make the part or have print errors that have been there since day one.
On the other hand several of the casting guys put a lot of effort into updating and correcting stuff Like Maury of lone star and cambel roberts -gade and the midwest model -tom thumb are really nice castings.
 

Allan Crook

Subscriber
Last Subscription Date
07/26/2020
Re: Machining castings.

Hi John

It sounds like they know of the problem since they are happy to replace the castings. I have not much experience, but with the castings I have worked with when I find any problems with my castings the suppliers are happy to replace them and so I would take them up on the offer. As with any engine the dimentions are critical to the overall performance of the engine after all they are in thou of an inch so missing material or in your case mass from the flywheel will have a detrimental effect on the operation of the engine.

Regards
Allan Crook
W&S 7985
 

OTTO-Sawyer

Subscriber
Age
57
Last Subscription Date
07/15/2019
Re: Machining castings.

...My problem is that there is insufficient metal in some of the castings to achieve the dimensions shown in the drawings. e.g. flywheel diameter and width of face, length of cylinder bore, etc. I realise these dimensions are not necessarily critical (e.g. the piston misses the head by around .5" at tdc!) but does this not defeat the whole object of working to drawings? Or am I being too fussy?
I have spoken to the suppliers, who said it wasn't critical ...

John Fearnley.
With the amount ($$$.$$) you pay for castings, there's nothing wrong with being critical when they aren't made right. You paid for a quality casting not the scrap value for the weight of the iron.

If you're building an out of production model that parts aren't available for anymore you either have to deal with it by altering the dimensions or find a foundry and have the parts recast yourself using the bad one as a pattern with some bondo or other material added to make up the size difference.

If you're dealing with a company that's still in business, I would expect them to replace the bad parts at no expense to you as long as it's their problem and not something you machined wrong.
 

Ken K

Registered
Last Subscription Date
03/03/2017
Re: Machining castings.

I bought a Red Wing kit five or six years ago, when it was still sold by Red Wing. The head was a little rough, and I thought i would use the CNC mill, to clean it up. Using the dem. on the drawing, all I cut was air. Called and asked for a casting that had the stock that I could use to cut to size. Was told the casting I had was the standard they used, that was the only size.
I second the comment about the Tom Thumb, 1/2 scale Gade, Lone Star Engine (Muarys) kits. Built number one of Maurys Marion. It had some problems but he worked with me, to get the drawings right, sent me corrected drawings, and replaced one casting, to correct a problem. I can not say that about a lot of other engine kit makers, I have bought from.
When you go to a model engine show, ask the guy who built the engine, on the table, what he thought about the kit. Good way to find out about good/bad kits .
Ken K
 

Jeff Smith

Registered
Last Subscription Date
08/05/2018
Re: Machining castings.

I have a small business and it involves the construction industry. I prepare site plans and other various plans and I draw them myself in AutoCAD. I PRIDE myself in my work and the talents that I have been blessed with, and I do get my butt out of the chair and leave the office to make numerous site visits during the design and construction phase unlike many others in my profession. I do it for many reasons, but my biggest pet peeve is that a set of plans that are not highly detailed and accurate are 100% WORTHLESS to the General Contractor and all of the Subcontractors!!! Yes, things do change in the field occasionally, but that is usually due to the property owner making the mistake of giving the power company or phone company a blanket easement for the property and when that happens all heck breaks loose because they just come in and plow up the site and start placing “their” items where they please so it causes other items to not work, that is why I encourage the client at the beginning to provide easements in locations that WE designate and they must adhere to them or pay the cost to correct their mistakes. On almost all of my plans, in the end, I am able to do a “save as” and change the title to “As-Built”, change the date and make a few minor adjustments and the owner has a set of plans with all items in their exact locations so 10 years from now they know where item “x” is buried…………………………

On the hobby/engine related items I have drawn and built, once completed, I did go back and “correct” my plans with my “as-built” that I kept while working on the project because if I have to fix something or make a new piece for some reason in the future, plans that are not accurate to me are USELESS and time, effort and expense totally wasted. If my children show an interest in the item and want to make one someday they will have accurate plans to build a new one or repair the one I built.
I am rebuilding a 7-1/2” gauge 1-1/2” scale locomotive right now and the plans are totally USELESS. I do however, now have a set that I have red-lined from the existing parts that appear to be more RED than black and white when looked at from a distance.

Just my opinion…………………….but inaccurate plans are useless and make good starter paper for firing a steam boiler………….…………………
 

Manorfarmdenton

Registered
Re: Machining castings.

What a helful response! Thanks everyone for taking the trouble!

The situation with the Red Wing kit (I gather) is that it is sold in the US by P.M.Research, who have their name on the drawings. Their castings may well be fine. I bought my kit from Engineers Emporium here in the UK, who say they have sold 450 sets of castings without any problems arising. When I contacted P.M.Research about the skimpiness of the cylinder block they told me the castings from E.E. were made in the UK and didn't want to know. I now realise the official importers of Red Wing kits from P.M.Research are Forest Classics www.forest-classics.co.uk and had I bought from them I would have had US castings to go with US drawings. Possibly the problem would not then have arisen, but at the time I hadn't heard of Forest Classics.

Thanks again for the support. I have to say I find It a bit disappointing to be working to a thou or two for the first time in my life, and then having to accept the dimensions I end up with! I've done that all my life - I was hoping this exercise would be a bit more professional!

I'll keep persevering and perhaps post some photos of the engine as it comes together, if anyone is interested. John.
 

Manorfarmdenton

Registered
Re: Machining castings.

<<If you're dealing with a company that's still in business, I would expect them to replace the bad parts at no expense to you as long as it's their problem and not something you machined wrong. >>

Otto, I have a feeling the patterns are skimpy as they say the 8.2" diameter on the drawing isnt critical!

---------- Post added at 01:59 PM ---------- Previous post was at 01:52 PM ----------

<<in your case mass from the flywheel will have a detrimental effect on the operation of the engine.>>

Allan, I quite agree. In fact the drawing says the scale size is 8" but make them 8.2" as it makes the engine run more smoothly. Engineers Emporium dont think the size is that critical. As much as anything, I am disappointed that I can't make my model exactly to the drawings, which must surely mean a shortcoming with the castings! Unfortunately I have spent too much time boring the cylinder, milling the base etc to want to ask for a refund. John.
 

OTTO-Sawyer

Subscriber
Age
57
Last Subscription Date
07/15/2019
Re: Machining castings.

Just a thought.... if it's the flywheel diameter that's not cleaning up and you want to make it bigger, maybe turn it 1/4 to 3/8 undersized and then turn a stainless steel or brass ring 3/8 to 1/2 inch thick .001 - .0015 smaller on the inside, heat it up to expand it and press it over the flywheel casting then finish turn it & polish the rim. Or make the ring out of steel to keep the cost a little bit lower if you plan to paint it.
 

jonathan g

Registered
Re: Machining castings.

hi there
i have built a redwing and also live in the uk so if i can help with anything please ask.

as to your castings you paid good money for them so they should be correct!!

jonathan
 

Manorfarmdenton

Registered
Re: Machining castings.

Hi Jonathan,

I think I have resolved the issue with the flywheels as Engineers Emporium have replaced the original castings and agreed that one at least was less than perfect.

Thanks for the offer of advice, which I'll take you up on! One question I have is why are there two cast piston rings and an o ring in the kit? The drawing shows three ring grooves, so presumably the o ring fits in the lowest one does it? I have seen mention of an oil control ring, but am not sure why one is necessary on an open-crank engine!

Are you happy with your Red Wing and its performance?

John.
 

Forrest A

Registered
If you are making a hit and miss engine, for best coasting/least drag, use only one ring. Also if you use Colman gas/WD-40 mix (15%, what most model engine builders use) you will not have any worries about oil either.
 

SDP

Subscriber
Last Subscription Date
07/14/2019
Coleman fuel contains Naptha petroleum....how much?....doesn't really say...Anyone up for some bacon?
 

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