Brassy babe engine - beginners questions

[student123]

Hello,

I'm new to model engineering & based in the UK. For a first project picked the brassy babe engine:

http://www.davegoodfellow.com/plans.pdf

There are some things I dont understand:

1)what are the screw thread types intended when it says "tap 4-20" and "tap 2-56". Myself & the man at my local tool store managed to find a 2-56 as a UNC but couldnt find 4-20.

If the screw threads are obscure, so I dont buy taps I many never use again, would there be a metric equivalent I could switch to ?

2) What type of loctite glue is meant?

3) I have a bench drill , but no countersinking tool/bit for this project - what do I need to get?

Mike

 

[shred]

The good thing about the Brassy Babe (and most other wobblers) is not so much is critical besides the port locations and pivot points-- the threads certainly aren't-- using whatever metric is reasonably close will be fine-- there should be a 'closest metric thread' topic on here somewhere. I think by 4-20 he meant 1/4"-20, but those intake and exhaust fittings could be soldered in or loctited or whatever if you prefer (mine are threaded but not loctited). By Loctite he probably means the regular threadlocking adhesive; some of the Brits will no doubt know the local trade names and types. There are a zillion types, some better than others for this purpose. I used some #620, but only because a friend gave me a little bottle as it's not in most hardware stores-- superglue or epoxy would probably work almost as well. For the countersink, he means a flat-bottomed hole the spring sits in. I used an end-mill on mine, probably 3/16", but it might be doable with a drill, or even skipped and left for later since the spring and bolt won't be in the way of anything unless you make a very large flywheel.

 

[Groomengineering]

Hi Student123!

If you would rather use metric 2-56 = .0860 so an m2x.04 (.0787) or an m2.5x.045 (.0984) would work. 4-40 = .1120 so an m3x.05 (.1181) would be spot on.

Jeff

 

[mklotz]

You may find this useful...

	British Association			Closest American
   	   Threads				  Threads

	BA 	 OD	TPI	PITCH		THREAD	 OD
	Size	(in)		 (mm)			(in)

	16	0.031	134.0	0.19
	15	0.035	121.0	0.21
	14	0.039	110.0	0.23
	13	0.047	102.0	0.25
	12	0.051	90.9	0.28		0-80	0.060
	11	0.059	82.0	0.31
	10	0.066	72.6	0.35		1-72	0.073
	9	0.075	65.1	0.39
	8	0.087	59.1	0.43		2-56	0.086
	7	0.098	52.9	0.48		3-48	0.099
	6	0.110	47.9	0.53		4-48	0.112
	5	0.126	43.0	0.59		5-44	0.125
	4	0.142	38.5	0.66		6-40	0.138
	3	0.161	34.8	0.73		8-32	0.164
	2	0.185	31.4	0.81		10-32	0.190
	1	0.209	28.2	0.90		12-28	0.216
	0	0.236	25.4	1.00		1/4-28	0.250

 

[Groomengineering]

Quick question, hopefully without going too far off topic, are BA and BSW still used 'over there' for anything but model engineering or has it all gone metric?

BTW - Welcome to the forum Student123! Two rules - have fun and th_wwp !

Jeff

 

[rake60]

The plan states:
"Drill 1/16" X 7/16" hole "A" and countersink 7/32" X 1/4" deep.
Tap 4-20 for inlet and exhaust tubes."

I believe shred is right on the thread. It should be 1/4"-20.
The "countersink" is just a 7/32" drill to open the 1/16" hole
up so it can be tapped for the inlet and exhaust tubes.

Rick

 

[bearcar1]

Hello Mike and welcome. wEc1 If I may, allow me to address your questions.
1) The reference to (tap xyz) means to cut internal or external threads in that {xyz} size by the use of either a thread tap for internal or a thread die for external applications. You could substitute the nearest metric equivalent for the sizes that are listed on your drawings, just be sure to make the same changes on the mating parts. A listing of imperial tap sizes and their equivalent metric sizes is available by doing a search for thread size conversion.
2) Loctite (which is not really a glue) is a product that is applied to a part that is subject to vibration or has no mechanical means of staying in place, such as a pin in blind hole. (there is nothing securely holding the pin in the hole other that friction itself) These products come in a variety of formulas. Some are listed as thread lockers and are used primarily on bolts to keep the associated nut from vibrating loose, with this type of formula the parts can usually be disassembled simply by using mechanical force ei: a wrench. Other formulas are more robust and require the use of a surface catalyst before the product is applied and the parts to be joined are affixed together. This type of formula usually requires either a solvent or the application of high heat to separate the joined pieces. Read the applications specs that come with the product to determine if that product will be suitable for the application. "Loctite" is a brand name and they have a website that lists all of their product line and lists all of the specifications and applications.
3) Not having a countersink is not the end of the world but having one does make life a bit easier and they are not that terribly expensive. A drill bit that is the diameter of the screw to be countersunk 'can' be used in a pinch but utmost care and diligence must be used when doing so. The part should be securely fastened to the table of the drill press and after the through hole has been drilled the selected bit should be immediately followed up with in order to obtain concentricity. The next through hole drilled and the bit changed out to the larger one and the process is repeated. The use of a proper countersink will eliminate the chances of the piece getting 'grabbed' by a regular drilling bit thus avoiding a damaged part and potential bodily harm. "The right tool for the right job" as the saying goes.
I have addressed all of your questions now and am certain that you will have others, this is the place to air them out and the best of luck with your project.

Jim B.

 

[Metal Mickey]

Good answers so I will only say welcome!
Metal Mickey

 

[Groomengineering]

Oops.. dyslexia got me again ;D OK 1/4-20 = .2500 so m6x1 (.2362) is as good as it gets. As shred pointed out though, it would be fine just to solder or glue the tubes in.

Jeff

 

[zeeprogrammer]

Welcome to the forum Mike.
No surprise to me that you got such great responses and detail...it's a great forum.

 

[doc1955]

Just a point Loctite is not a glue or adhesive it is an anaerobic it sets up in the absence of air.
When you use the permanent bearing or bushing mount you will get a fit (when used with a slip fit) much stronger than any press fit.
What it does is fill the microscopic grooves in the material and set up and the shear strength is much higher than a press fit.
So if you have Loctite just make the tubes a slip fit and apply Loctite and some primer (primer will cause Loctite to set full strength in a very short time but not necessary) and you should be set.

 

[student123]

Thanks to all of you who replied. Great to get both quick & detailed responses, means I can move things along this weekend.

 

[Metal Mickey]

Re the glue question, I was never impressed with the success I got with anaerobic type adhesives until I saw some advice re cleaning prior to use. It is most important and makes a bug difference. If its a small assembly I use an ultrasonic cleaner I have or else cellulose thinners, there are specialist cleaners as well.

Ever since I prepared well (as in all things really) I have had far better results.

MM