Shellac Mandrels and Chucks.

[Tony Bird]

Hi,

I have just started making a Stuart S50 mill engine. When making an engine from castings I often start with the cylinder and members might be interested in my approach. Having filed off any casting joints which on Stuart castings are very small I just flatten off the port face.




The cylinder is then bored and its one end cleaned up but not to size.



A piece of mild steel is centred both ends and set up between centres in the lathe. It is then turned to a good slide fit in the bore of the cylinder. Then shoulders of the same diameter are turned one at each end of the rod leave a raised portion which is less than the length of the bore of the cylinder. This raised section has several grooves cut in it.



This rod is then heated and shellac melted on to its. the cylinder is also heated and fitted over the rod. The shellac when cool will hold the cylinder in place.



The result can then be set up between centres and the cylinder machined to size.



The cylinder and its rod can then be removed from the lathe and mounted in the mill to do its flat surfaces.




When finished the combination can be heated and the rod can be removed from the cylinder. This has not been done as the steam chest and cover will be attached for machining.



A lot larger cylinders can also be done in this fashion. One I did as a demonstration for my model club. The ones on my 5" gauge locomotives were done the same way



The more usual way of using shellac on a disc chuck.



Hope this is found interesting.

Regards Tony.

 

[starnovice]

Where can you get that type of shellac?

 

[tornitore45]

I assume the grooved mandrel slip fits the bore to define center.
What is the purpose of the grooves?
Is shellac loaded into them?
From the picture I can only see the shellac on the outside.

 

[phrodo]

I have also used stuff called blocking wax. It's used by lens grinders to hold a piece of glass on to a plate or mandrel so it can be polished. Same idea, heat everything with a heat gun and let it flow together. When it cools it's not going to come apart easily. Great for holding thin sections or bigger parts that have to have at thin section milled in them. Just like the shellac method the beauty is that the part is perfectly held with no distorting forces.

 

[enfieldbullet]

shellac can be bought from art supply stores.

nice example of application, great pictures! thank you!

 

[Tin Falcon]

I do not expect it is any sort of special shellac. I buy bulls eye brand at the local hardware store and home center.
Tin

 

[Mechanicboy]

I used locktite as clue when i turned the cover for steam chest for Stuart compound.

 

[Sshire]

Regular per-mixed shellac, like Bullseye, is shellac flakes dissolved in alcohol. Think I'd want to mix a much more concentrated shellac that would be very viscous.
The optical blanking wax mentioned earlier, comes in various holding strengths.
In my experience, the Stronghold blanking waxes, hold exceptionally well. The same company makes a "Blanchard Grinding Wax" which is actually for the initial rough shaping of lenses. Holds like epoxy. Heat gun and it's released.

 

[Beachside_Hank]

That's a great tip, but furniture and cabinet grade shellac is priced at a premium nowadays as the last few seasons harvest are reported to be very sparse. I'm just about out of mine, it is my goto problem solver for a lot of applications and even in flake form it only has a shelf life of about a year or so. I wonder if hot melt glue would work the same.

 

[phrodo]

Just realized Stronghold is 15 minutes down the road. Check their website, they have a sample kit they they'll send out for free. Might be just the thing if you only need a little bit on occasion.

 

[Tony Bird]

Hi,



Where can you get that type of shellac?

Here In the UK I get it from a Horological & Jewellery supplier Cousinsuk.com. It comes in sticks either refined or not, either work, I recently bought some 200grms (6oz ish) of unrefined for £4.50.

I assume the grooved mandrel slip fits the bore to define centre.
What is the purpose of the grooves?
Is shellac loaded into them?
From the picture I can only see the shellac on the outside.

Sorry I didn't make this clear. Yes the grooves in the mandrel are charged with molten shellac before sliding the cylinder on. What can be seen in the photograph is the overflow of shellac.

I have used the furniture trades shellac flakes by meting the flakes in a small pot/tin and spread it on the chuck with a hot pallet knife. Solid shellac does not seem to have a shelf life.

I forgot to mention that after the work piece from the chuck any residual shellac can be removed by placing the work piece in alcohol.

Stub mandrels can also be used in blind holes but they have to have a hole drilled through them to allow the air out. This works really well for things like pump bodies and thin wall displacer pistons used in Stirling engines.

Regards Tony.

 

[Mosey]

I have used the 3M double sided adhesive tape designed for this purpose for small thin parts on the mill with limited success. It will not hold under heavy cuts. It is pricey, and hasn't worked well. I'm sure I could improve my method, and may try it again. One problem is removal after machining, difficult.
Mosey:fan:

 

[dondoerner]

Have you tried Resin from the Archery shop used to hold the nock onto the end of an arrow shaft. It works very well for me. Also requires heat to hold and release. Donald C Doerner CET

 

[goldstar31]

Shellac is part on what used to be used to make wax chucks.
It was added to the wax to give a slightly higher melting point and to give a bit of body. I recall that Tom Walshaw as Tubal Cain wrote up a recipe.

Again I used to get tubes of the stuff from Black and Decker to stick sanding disks onto faceplates. Probably, I still have some lying about.

Today, I would suggest that the most useful stuff is the translucent glue sticks and their heat guns. Far cheaper and far more available!

As for the removal of sticky stuff from tape, I'd suggest either 'sticky stuff remover' which is probably orange oil or WD-40. Frankly, I have never had any faith in the double sided tape for surface grinding. I find( or don't find) bits which have 'come loose' like missiles.

I bought a trio of magnetic tables and chucks. One I like, I got it given as a present with my Clarkson tool and cutter grinder. It is round and energises with an electric switch and is ideal for scraping slides etc.

Recalling Tubal Cain, he designed something called a 'thin piece vice' which was mechanical and this appeared in one of his books with wax chucks and a massive Gibraltar tool post for the Myford.

A hint to some- about shellac. Age and heat change its properties.

 

[Tony Bird]

Hi,

A hint to some- about shellac. Age and heat change its properties.

Just curious what happens to the shellac?

Regards Tony.

 

[goldstar31]

I'm somewhat surprised at the question but shellac is one of the constituents of paints and varnishes.

Just another hint- it goes into some abrasive wheels as the binder.

Basically- all the oils and whatever change their state.

Which reminds me- the impellor pump on the dishwasher has cracked into a thousand bits - plasticiser has gone. I'm 83 and I'm shrinking- plasticiser going. Tedious, Tony- but true.

Regards

Norman

 

[Mosey]

Which Loctite?

 

[Mechanicboy]

Which Loctite?

Blue treadlocker. Apply on the part and mount to the disc, let it stay 5-10 minutes under press from tail dock before work. Take light cut each time. After use, heat up the part to dismantle from the disc. Not tried on bore/shaft due i am not sure i can dismantle the parts each other.

 

[Tony Bird]

Hi,

There is at least one area that shellac might have an advantage over other forms of sticking parts to be machined on face plates.



It allows the work piece to be centred about a hole. This requires that a extended wax chuck is made that allows a blow to be played on the back of it. The work piece is held to the chuck in the usual way and is allowed to cool until it is held, while still hot it is put in a 3 jaw chuck and its back heated until the shellac becomes mastic again. Using the set up shown above the work piece is centred while it is rotating, it is rather like a potter throwing a pot.




A sort of reverse of the mandrel type wax chuck can also be made and used to put '0' ring grooves in pistons while on their rods.












Regards Tony.

 

[MachineTom]

After reading the thread, I dropped an email to Stronghold, and received a nice sample kit, of different blocking waxes. I'll be making a test shortly on holding some SS washers in the SG.

Its why these forums are so good.