Help with reading dimensioning

[Gilrock]

I'm working on my first small engine project and just learning to use my new metal lathe. I got the plans for the Launch Engine from littlemachineshop.com as a starter project for learning. On the cylinder head a fitting screws in at the top side. The drawing says ".22 DIA. Spot Face to Full Circle". I'm pretty sure I need to bore in till I have an edge all the way around the circle. My question here is does the bottom of this need to be flat? I was thinking it did and not sure what to use to do this. A drill bit would leave a taper at the bottom. Do I need some type of end mill bit?

I can figure out most of the dimensioning but what does it mean when there is an angle "V" shape touching a part with a number like 32 or 64 in it?

Thanks,
Gil

 

[rleete]

Yes, you need a flat bottom on a spotface. Ususally it's a seat for a mating part; in this case the steam port/tube. Use an end mill for it. A 1/4" should work, just leaving a little more of a flat around the part. You could also make the fitting slightly larger to fill it up.

The "V" is a finish mark, and denotes the surface roughness. The number is the roughness in microinches. Smaller numbers indicate smoother surfaces.

 

[90LX_Notch]

Gil-

If you use an endmill make sure it is center cutting. Not knowing what the part actually looks like, if you can hold it in your lathe, you can you create the spot face using it.

rleete has it right. It's the Surface Finish expressed as the Mean Average in micro inches of the peaks and valleys of the finish on the part. Think of it like this- If you sanded your part with 100 grit paper the scratches in the surface would create little peaks and valleys that are measured in micro inches. If you sanded the part with 800 grit paper, the peaks and valleys would be less micro inches in height. Therefore, the Surface Finish would be better, thus producing a smoother finish.

-Bob

 

[gmac]

Gil;

These links may help you with the issue of surface finish on drawings.

http://www.engineersedge.com/surface_finish.htm

http://classweb.intelliteccollege.com/VideosB/Drafting/ResourceDocuments/11.PDF

Cheers Garry

 

[rake60]

Surface finish requirements are often exaggerated on drawings.

Cheap, simple comparators can be purchased to give you an idea if what they should be.

Here's is one vendor who carries them: Link Here

Rick

 

[Tin Falcon]

The US standard is Gar they are over $ 75 new from enco and others

You can also get metal import ones here
http://www.use-enco.com/CGI/INSRIT?PMAKA=615-6580&PMPXNO=949128&PARTPG=INLMK3

The plastic ones are more than adequate for the home shop . unless you have hardened finger nails the plastic ones should last a long time . and easily replaced if worn.
I have a plastic one and a gar. IIRC I paid under $30 for my gar used befre a lot of metal prices went crazy.The plastic one was part of the contents of my used kenedy.
Tin

 

[Gilrock]

Thanks for all the help. I'm a rookie but a fast learner. My engineering degree is in electrical but I've mainly done software development for 25 years. I've always wanted to learn how to machine metal parts. The part I needed to drill the spot face is where the tube is entering the cylinder head in this project:

http://www.littlemachineshop.com/products/product_view.php?ProductID=3135&category=1963256891

I did get a 4 jaw chuck with the lathe but not sure I'm ready to try to offset mount this piece to drill this hole.

My biggest challenge so far has been trying to part off pieces when they are almost done. I've already had one part ripped out of the chuck and tossed onto the table. I was able to recover that piece but the diameter is a little smaller than spec. but it didn't look like a critical measurement. Then today I spent 2 hours making the shaft for this thing where I had to turn most of a 3/4" piece of steel into just under 1/4". Then trying to part that off the tool dug in and bent the piece. I got it bent back almost perfect. Now I'm shopping for a dial gauge so I can figure out where the out of round point is.

Thanks,
Gil

 

[rleete]

Chances are, you'll spend more time messing with it and never get it right. And, you'll create lots of frustration for yourself. Making scrap is part of the learning process. Toss it in the recycle, and start over. Chalk it up to experience. We've all been there and done it.

 

[AlanHaisley]

Sometimes you might want to part off with a hacksaw, chuck the piece from the other end, and face it in the lathe rather than attempt a complete cut with a parting tool. In fact, starting with a parting tool and finishing with a hacksaw and file can also work for you. For really skinny parting off, get a jeweler's saw whose blades have a bazillion TPI.
Alan

 

[Tin Falcon]

I'm working on my first small engine project and just learning to use my new metal lathe. I got the plans for the Launch Engine from littlemachineshop.com as a starter project for learning. On the cylinder head a fitting screws in at the top side. The drawing says ".22 DIA. Spot Face to Full Circle". I'm pretty sure I need to bore in till I have an edge all the way around the circle. My question here is does the bottom of this need to be flat? I was thinking it did and not sure what to use to do this. A drill bit would leave a taper at the bottom. Do I need some type of end mill bit?

I can figure out most of the dimensioning but what does it mean when there is an angle "V" shape touching a part with a number like 32 or 64 in it?

Thanks,
Gil

Gil first of all welcome. The purpose of a spot face is for a bolt head or screw head to sit flat. there ae two ways to make one 1 with a counter bore drill the hole first then counter bore. The problem woth this is if the surface is angled the bit will deflect. the second method is to use a center cut end mill . spot faces are also specified to give a flat spot to drill into.
As far as surface finish specs in the home shop only a basic understanding is really needed. In industry they communicate the level of finish needed or expected by the customer. The better the finish the more time and expense to produce. So surface finish is an important spec.
In the home shop you are the customer. Make the surface finish as nice as you like.
as far as holding cylinder heads look here.
http://www.homemodelenginemachinist.com/index.php?topic=18204.msg187698;topicseen#new
Also Z programmer did a detailed thread on building that engine from a kit . a long but worthwhile read for the newby.
Tin