Hey guys,

I need some help, ive been messing around trying to make a set of 1.5" sch40 merge collectors and theres a problem with my math.

Basically ive been setting the pieces in the dividing head on the mill oriented at the merge angle (which is 15 degrees in my case)

after making the first cut to the right depth (basically so the 4 pieces will leave a 2.5" outlet) im rotating the pipe 90 degrees in the dividing head for the second cut.

After doing this, i would expect to see a nice 90 degree external corner on each piece so the 4 pieces meet up nice in the middle, but instead im ending up with MORE than 90 degrees, so the 4 pieces together end up with almost 1/8" gap in the centre "star".

What am i doing wrong? Why is the angle growing to more than 90 degrees on the finished part?

I cant afford to buy off the shelf or I would, but the collectors would owe me more than the entire header fab and that aint cool and im kinda looking to know what im doing wrong with the math/angle rather than a recomendation on who to buy from.

cheers!

 

What machine are you using? Bridgeport? Is your table locked in x and y? is there enough slack to pull the table over slightly, either or both ways? Is the dividing head locked? Do you have the right plate on the dividing head? I run CNC nowdays, so I forget how many different plates you can have for a DH, but I do remember there are several. I would think a super spacer would be a lot simpler. I ran a Bridgeport one time that would jerk the table over a few hundred thousands, if you tried to climb cut. What a POS that thing was. Did you drill holes then run an end mill in? A 2.5 cutter is one huge cutter. I could see it pulling the head over, spinning the part in the chuck, and even jerking the table. Drill, end mill u/s, and then bore the holes, if you want them straight and on size. You didn't say if you are a machinist, so I have no idea if you know that, or you experience with manuels. I worked in job shops for years, and then went to a big company. They acted like normal procedure was rocket science.

To check for what's moving when you are cutting, remember to put indicators on the column to the table in x. Put one on the dividing head, and you could even run one from the column to the head to see how much movement you are getting. If you are using a long end mill, that sucker can reall pull over/flex when you are running it into the part. That will egg your holes badly.

 

Get us a pic of your setup and what you're getting. I'm with gremlin, sounds like something is moving on you, before going any further I would probably try locking as many of the axis and the rotary table before running a cut and see if it gets better.

 

hey guys, i was only using someone elses bridgeport and im not a machinists arsehole so in the end I burned up the time i had on it making incorrect fitting pieces and in the end I went home disappointed.

After swearing a bit (well, a lot) i made up some collectors with a 5" grinder, they dont fit as nice as machined pieces but theyll do the job.

Never did figure out why the milled bits were wrong but oh well.

Cheers guys

 

for trying. Most people would get scared and run away. Machining is a little tougher than most numbnuts think. The old saying is, If you want your parts fast, we can do it. Now, if you want them right, it's gonna take a little longer, unless you get the wand. I bet running a 2.5 em into that part took quite a while, and I'd bet that thing was making al kinds of noise, and jerking around.

 

I like to do work like that with a big shell mill, I have a 3, 4 and 7.5" Sandivik (they're actually metric sizes but that's close) shell mills that do this kind of thing really well if you can get them setup to make the cut. Also, the inertial of the great big piece of steel spinning (the big one is probably 30# or more) tends to deaden some of the vibration.

Sometimes the best way to hold something like that is to weld it to a heavy chunk of steel...