machining question??

[Dan]

I am brand new to running the lathe so I am creating a few projects for myself for practice. I am building an engine stand and have turned down some slugs for the parts where the engine block bolts to the "fingers" on the head of the stand. What size holes do I need to drill through the slugs to bolt the block to the "fingers" In other words, what diameter are the bellhousing bolts for SBC/BBC? I dont have any on hand here at school to measure for myself. I am not set up to bore holes so I want to drill holes just big enough for the bellhousing bolts to slide through without a bunch of slop. Thanks, this machining is kinda addictive!

[Hot Rod To Hell]

3/8" bolts

[36-3window]

SBC's use 3/8" bolts...i think fords are 7/16" ??? i drilled them out 1/2" on the engine stand i made

[Dan]

thats what I was guessing but wanted to confirm. Also, on the lathe to drill a 1/2" hole do I want to work my way up to that with smaller bits or can I drill the 1/2" hole the first time?

[Slag Kustom]

the bolts are 3/8 i would make the holes the next size up. (some sholder bolts are tight in a 3/8 hole)

[Unkl Ian]

Add 1/32" to the bolt diameter for clearance.It will make your life easier.

[Unkl Ian]

End face your parts,then center drill.

If the machine has the HP,you can drill 1/2" no problem.

If not,drill a 1/4" pilot hole thru,then jump to 1/2".

[36-3window]

[ QUOTE ]
thats what I was guessing but wanted to confirm. Also, on the lathe to drill a 1/2" hole do I want to work my way up to that with smaller bits or can I drill the 1/2" hole the first time?

[/ QUOTE ]

om my lathe , in solid bar stock , i would drill it out in several steps..start with a centering bit , then maybe 3/16-1/4...then 3/8....then 1/2 (or 7/16 if that is your final size)

keep in mine ,i'm not a REAL machinist either...good luck and have fun....you will be amazed what you can build when you have a lathe

[woodythx138]

When drilling holes it's important to do two things, if you are wanting a hole say 3/8" dead nuts then you would drill it 11/32 or 23/64 and then run a 3/8 ream through it and you have a perfect 3/8 hole. Now if you drill it 3/8 with a 3/8 bit , it will be already oversized to allow for the slop
you are looking for.Most standard drill bits will drill the size you want abit oversized, and if you want close tollerances then you step up to letter drills. Hope this helps. The G-Man Chris

[fab32]

I'd also recommend 1/2 holes for your engine stand. You never know what you might want to bolt to it and a little slop in this area is no big deal, in fact it can be a godsend when trying to get the 4 fingers aligned to the bellhousing bolt holes. When you first start machining you tend to try and keep tolerances too close, the secret is learning which things need/require tight tolerances and machine accordingly.
If you think your having fun with the lathe wait until you get your hands on a good mill (Bridgeport) and your mother/wife will never get you to come in the house. http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif

Frank

[Dan]

well, the work continues, I've come up with a few problems -
-anyone offer any tips or tricks,advice when facing a piece?
-when trying to part my 3/4 round stock with the cut-off tool I get tons of chattering and squealing and it leaves tool marks on the piece, what am I doing wrong?
Thanks-

[PDX Lefty]

Are you using a HSS or Carbide parting tool? What type of material, eg mild steel?
Carbide you can run fast with no coolant. HSS must be run slower with a coolant such as cutting oil. If using HSS you can even put the lathe in back gear to really slow it down. The tool must be square to the part and be perfectly centered or just a few thousandsands below center. Hope this helps.
Another option since this is not a precision part is to just cut it off in the band saw and then face that end.

[Zodoff]

When parting,Check the height of the edge on the tool. it should be at center of the workpiece,or slightly under. if its higher,the edge wont hit the piece first. This is if you have the adjustable kind of tool,ofcourse. Or check your speed one more time.

Z

[C9]

[ QUOTE ]
-anyone offer any tips or tricks,advice when facing a piece?
-when trying to part my 3/4 round stock with the cut-off tool I get tons of chattering and squealing and it leaves tool marks on the piece, what am I doing wrong?


[/ QUOTE ]

Lotta good advice here.
I go along with cutting the piece slightly oversized in a band saw and then facing.
Cut-off tools can be a pain in the ass many times and the smaller lathes can have the cutting bit dig in and get yanked out of the tool holder.
This happens most times when the cut gets down to a smaller diameter.
If you're gonna use a cut-off tool and the workpiece will be drilled do the drilling first and then use the cut-off.
In fact, I like to do the drilling before the facing off if the rough cut face is square.

Like was said, make sure the facing/cutting bit's cutting point is on center.
If your lathe has a 12" swing (which means 6" from ways to center of headstock/chuck/faceplate) you can use the handy 6" machinists ruler to center the tool.
Lay one end of the tool on a way and the other end up against the cutting bit that's right over that way.
Rock the ruler back and forth a bit and you'll see if the tool is centered or not. A lotta guys make a bit height centering tool, but this way works just as well.
Final test is if the cutting tool cuts all the material away when facing or leaves a small tit.
The tit can be knocked down with a file leaving a smooth and unblemished surface.

One small trick when facing with a carbide bit - which can break if you go past center when facing - is to back the carbide bit off as it hits center. Let the carbide bit get pressure from the opposite side of the workpiece and most times it will get the sharp corner torn off. Most times not a problem with a HSS bit.

One of the problems with using a cut-off tool is the normal rotation of the chuck/workpiece tends to suck the cutting tool into the workpiece - which as you can see creates problems. To this end many guys make a holder or if possible set the lathe up and do the cut-off deal from the opposite side of the workpiece than normal with the cutting bit upside down. This requires the lathe to be run in reverse rotation. Advantage here is the cutting bit will be pushed away from the workpiece instead of being sucked into it.
It's an ok way to go, but the cut-off tool works ok if the setup is stiff. That means snug or tight gibs and no rocking of the tool holder.


A quick and easy way to center the tailstock is to place centers in both headstock and tailstock.
Slide the tailstock up to where the centers points almost touch.
Lock the tailstock down - snug is close enough.
Place a razor blade between centers.
Advance the tailstock center with the handwheel until the razor blade is supported between centers.
If the tailstock is well centered the razor blade will be square to the world in all orientations.
If not, it will tell you which way to go.

Lindsay publishing has some great books on machining.
One good one is called "Advanced Machine Work."
The book written in the 30's has a lot of good info that us home machinist guys can use.

[oldspeed]

I agree a lot of good information is here, but cut off operations are the most dificult lathe operations. Need to be on center as most have said, I wouldn'r worry about being a little below because any movement in the ways or gibs will pull the tool down. The other thing you may want to do is get a copy of the "Machinery"s Handbook" it's been around forever and has thousands of pages of information covering everything from cutting tool geometry to strength of materials, probably around fifty dollars by now but worth it. Remember the key to good machining is rigidity and geometry of the tool.

[Digger_Dave]

Although a "parting tool" is an accepted method of cutting round stock in a lathe; another way is to use a hack saw!

I just finished cutting a number of pieces of mild steel round stock (1") and I don't have a power hack saw or a friction cut off saw.

I started by holding the length of bar stock (comming through the head stock tube) with the three jaw chuck; facing the first end, then moving the bar stock until the line of the next cut was sticking past the chuck about three inches.

Allowing for "cleaning up" the end, mark the stock with the tool bit that you will to face the ends. (a shallow grove is all it needs) Use a conventional hand held hack saw (I like a 12 ") and a 24 TPI blade INSTALLED BACKWARDS rest the blade in the grove, turn the lathe on,....

EDIT: RUN THE LATHE IN REVERSE!! (missed this important detail the first time!!)

...and start sawing. Don't hold the saw in ONE location. Move the saw back and forth just as if you were cutting the bar held in a vise. USE LIGHT PRESSURE UNTIL YOU GET THE FEEL FOR THE CUTTING ACTION.

You will get a fairly square cut and it takes a lot less time than try to cut the material in a vise.

[Unkl Ian]

[ QUOTE ]
I get tons of chattering and squealing and it leaves tool marks on the piece, what am I doing wrong?


[/ QUOTE ]

Probably running too fast.
Smaller machines lack the rigidity necessary to run cut off blades fast.

Slow it WAY down,150-200 rpm MAX.
Make sure the sharpened cutting edge is at center height,and at 90 degrees to the part.
Add coolant as required.

[Hot Rod To Hell]

Hey Dave, why do you install the blade backwards??? I use a hacksaw with my lathe the same way I cut anything else and it works great! http://www.jalopyjournal.com/ubbthreads/images/graemlins/crazy.gif

[Flexicoker]

On the cut your making with the cutoff tool how far out is that from the chuck? if its hanging too far out that could be causing the problems as well

[ray]

i dunno his intentions, but i would do it that way running the lathe in reverse, so it pulls the hacksaw away from you rather that pushing at you, in case "something" happens. that might be his reason for installing the blade backwards.

the hacksaw is a good idea, parting off if one of the worst operations, even for experienced machinists.

[Dan]

some great tips here! glad to here parting off is difficult, I was starting to get kinda cocky thinking I was getting the hang of it and then hit a wall when I tried the cut off tool-

[Digger_Dave]

[ QUOTE ]
i dunno his intentions, but i would do it that way running the lathe in reverse, so it pulls the hacksaw away from you rather that pushing at you, in case "something" happens. that might be his reason for installing the blade backwards.

the hacksaw is a good idea, parting off if one of the worst operations, even for experienced machinists.

[/ QUOTE ]

HRTH and Ray; you guys caught me!! http://www.jalopyjournal.com/ubbthreads/images/graemlins/blush.gif http://www.jalopyjournal.com/ubbthreads/images/graemlins/blush.gif

I accidently left out the part about running the lathe in REVERSE when using the blade backwards!! http://www.jalopyjournal.com/ubbthreads/images/graemlins/blush.gif

Saves accidently getting the saw in the GUT!!