Machining help

[Thorpydo]

Ok, This is a project for the TMCC, http://www.automags.org/forums/showthread.php?s=&threadid=56397, and another project of mine.

Anyway, I'm having a bit of trouble drilling a hole through some round stock and getting the results I want. To aviod any questions that might be asked later, I'll give you more information rather than less. The rod is clear polycarbonate(lexan). 1"OD ~5" long. I'm drilling a 11/16 hole all the way through. I'm first getting the center on my lathe and then drilling the hole on the drill press (My lathe is too small to drill hole on lathe). I've got a normal vise and a V-block that I'm using to hold the piece. I don't know the RPM that I'm using but I'm guessing around 800? I can check tommorow. I am also using windex for cutting fluid (as suggested by someone on here). I am not working my way up in drill diameters but will try that as well as using normal cutting fluid.

The problem that I would like to fix is the white rough spots on the inside of the bore. They don't have to be completly gone as I am going to ream and polish the inside of the hole but they need to be alot less severe then they are.

I'm guessing they are caused by either heat or chatter? On occasion, while drilling, it will scream like theres chatter but it doesn't do it all the time when the white rough spots are made.

Got any ideas/solutions/causes?

Thanks

PS... I just realized how ****ty of a photographer I am. I was trying to center the workpiece here...

[Thorpydo]

On that last one, where it looks like glare, its the white rough spots, I know these dont help much because the quality is terrible, but oh well...

EDIT:
Oh, btw, does anyone have any tricks to get the workpiece centered to the bit? I tried putting a live center in there, it worked ok.

[SocialD]

I'm not sure that this will help, but did you try grinding a different angle on the tip of your drill. I.E. The normal included angle of a drill is 118° try something closer to 90°. I'd try running the spindle speed closer to 500 rpm. Other than that just mess with your feed rate. I'm assuming that your drill press doesn't have power feed, so this will be tough. One other thing that I'd try is to add some relief to the drill. I'll try to post a pic to show what I mean. I think part of the problem is that the o.d. if the drill is rubbing instead of cutting.

[ignatz]

I've done quite a few projects with acrylic for my reef hobby from complete fish tanks to various bit and pieces.
In my experience working with acrylic, I found the following:

1. Don't use Lexan. Its harder to cut and shape than Plexi-Glass. Additionaly, it doesn't work with the acrylic bonding agent (Don't know if this matters or not.), doesn't flame polish very well and is actually a little more expensive.
2. You need special bits to cut plastic. When I cut Plexi, I use a saw blade that cuts and sands at the same time. I am fairly certain you can find drill bits that will do the same thing or at very least work to remove the hot acrylic while cutting. Look around, worst case scenario try a masonary bit since standard drill bits don't channel the molten plastic away very well.
3. Never use Windex on acrylic. It causes the material to spider and haze. If you need to use something to help with heat, try anti-freeze. When I have to cut holes through acrylic aquariums, I mark the spot for the hole then from the center point I make a circle (larger diameter than the hole I will cut) out of silicone so that it forms a basin. I fill the basin with anti-freeze and then cut through the acrylic.
4. Contact your local plastics store. They typically have the tools and chemicals you'll need to work with acrylic and stock tubing that might fit your needs. Let your fingers do the walking.

HTH

[chizle97]

Im not very informed on these type of things but it helps to use a jet sprayer to spray water on the part you milling, it would lower the temp of the metal which would make the milling look smother

[Thorpydo]

Thats how the 'pros' do it, but I believe there pretty expensive, depending on what you get.

I might just end up making it out of aluminum. Wouldn't have as much of the coolness factor going though.

[Catch22]

Did you know there is going to be a car named "ramrod"?!

[bjjb99]

Originally posted by Thorpydo
Ok, This is a project for the TMCC, http://www.automags.org/forums/showthread.php?s=&threadid=56397, and another project of mine.

Anyway, I'm having a bit of trouble drilling a hole through some round stock and getting the results I want. To aviod any questions that might be asked later, I'll give you more information rather than less. The rod is clear polycarbonate(lexan). 1"OD ~5" long. I'm drilling a 11/16 hole all the way through. I'm first getting the center on my lathe and then drilling the hole on the drill press (My lathe is too small to drill hole on lathe). I've got a normal vise and a V-block that I'm using to hold the piece. I don't know the RPM that I'm using but I'm guessing around 800? I can check tommorow. I am also using windex for cutting fluid (as suggested by someone on here). I am not working my way up in drill diameters but will try that as well as using normal cutting fluid.

The problem that I would like to fix is the white rough spots on the inside of the bore. They don't have to be completly gone as I am going to ream and polish the inside of the hole but they need to be alot less severe then they are.

You mention that your lathe is too small to drill the hole you want. Since you are able to use the lathe to find the center of the part, I assume by "too small" you mean "not powerful enough". Have you considered drilling a smaller hole, maybe 1/2" diameter on the lathe and then bore it out to size using a small boring rod? You might be able to get around any power issues by taking lighter cuts when boring than you could by using progressively larger drills. What kinds of tolerances are we looking for in the hole?

BJJB

[Thorpydo]

I don't mean power when I say small.

The drill bit I'm using is 11/16. It's also about a foot long and a MT3. I don't have enough distance on the ways for the piece and the drill bit. My tailstock also is only a MT2, so that drillbit is really not going to fit.

I would like +/-.001. We will see how it comes out after I ream the hole. Try #2 is going pretty good. Really slow 100-200 RPM and I'm feeding it really slow too. The white crakes are showing up but I don't believe they are as deep. They should come out after reaming(crosses fingers).

Oh, and also I think the hole would be too deep to bore. Its about 5 inches, would make the setup really unriged.

[bjjb99]

Originally posted by Thorpydo
I don't mean power when I say small.


Okay. Small means physically small, not underpowered. :)


Originally posted by Thorpydo
The drill bit I'm using is 11/16. It's also about a foot long and a MT3. I don't have enough distance on the ways for the piece and the drill bit. My tailstock also is only a MT2, so that drillbit is really not going to fit.
[/B]

A bit that long may be oscillating in your drill press. Since you're using a nearly foot-long bit, I assume that you've had no luck finding a shorter bit (six inches or so) that would fit your lathe. Would a shorter bit allow you to use the lathe instead of the drill? If the outer surface of the rod has been turned down slightly so that it is truly circular, you might even be able to make do with a three inch bit on your lathe... drill from one side, flip the part over and drill from the other, and finish with a reamer and then a good polish?


Originally posted by Thorpydo
I would like +/-.001. We will see how it comes out after I ream the hole. Try #2 is going pretty good. Really slow 100-200 RPM and I'm feeding it really slow too. The white crakes are showing up but I don't believe they are as deep. They should come out after reaming(crosses fingers).
[/B]

I couldn't tell for sure from the pictures... which way are the cracks running? Are they running along the rod's axis, or are they circular? If they're along the axis, it may be the drill is trying to expand the hole after it's been cut and cracking the surface. A reamer may well cut through those cracks, but it may also create additional ones.


Originally posted by Thorpydo
Oh, and also I think the hole would be too deep to bore. Its about 5 inches, would make the setup really unriged. [/B]

Yeah, I thought as much. That's why I was asking about tolerances. If you could stand looser tolerances than +/- 0.001 then a bore that long might be okay. Taking a page from my text above, could you drill out to, say, 9/16, chuck the part up in the lathe, and bore the remaining 1/16 inch radius using light cuts and only going 2.5 inches from either end of the rod? That would make your bore more rigid. I know rigidity starts to go away once you've gone beyond a couple/few tool diameters, but light cuts and the right shaped tool tend to help that issue.

When drilling holes in glass we used a piece of brass rod tapered to a fairly broad point and coated in a slurry of coarse polishing grit. Could a similar technique be used here? Maybe drill the hole undersized, fashion a slightly tapered rod, coat it in coarse grit, and use it to essentially grind your way to nirvana? It might take a while, but you may eliminate the cracks altogether since you're essentially polishing the part as you go. You may have to replace or reshape the grinding rod a couple of times since you're reducing it's diameter at the same time you're enlarging the hole in the lexan. If you have some spare lexan rod, you might even be able to use that for the grinding rod... eliminates the possibility of metal being deposited into the scratches left by the grinding.

Let us know how well attempt number 2 turns out. I'll keep my fingers crossed too.

BJJB

[Thorpydo]

Attempt two failed also..

But I'm learning some everytime.\

Ok, here's what I noticed and possibly an explantion of the problem?

-The 'cracks' arn't really cracks. I'm pretty sure they are rough areas where the bit isn't cutting, just kinda smudging the part.

-There is a definate pattern to the rough areas. They don't start right away; maybe once I'm an inch down. They make a spiral in the same direction(and I'm pretty sure with the same distance between flutes/rough areas) as the drill bit.

-The hole is definatly bigger where the rough spots are(I could feel this just by sticking my finger down the hole)

-As I was cutting, the bit and piece would move around. I can't remeber if they made a circular pattern or if they made a line back and forth. They moved quite a bit. When I wasn't cutting but the drill press was on, the drill wouldn't make the same pattern.

On both pieces I've used a center drill to mark the center and get the bit going. When I'm setting up the piece to drill, I get the bit and piece lined up pretty well, but not perfect. Maybe this is contributing? Also I've havn't been working my way up with drill sizes. Maybe I'll work my way up on the lathe, and then take it to the drill press for the final 11/16 hole?

You mentioned oscillating, I think this is whats happening. And also even if the drill bit was smaller it is a MT3 taper shank, and my tailstock is a MT2. I have also have a regular 11/16 chucking bit but that wont fit in my chuck.

Also, when I reamed the hole the reamer didn't follow the center, it cut off to one side. I don't want to talk about too many problems at once, but I think the cause of this could be that I can't get my reamer to chuck straight and so it moves around some when the drill press is on.

Thanks, long post, but I wanted to be descriptive.
Might take a picture of try #2 and post.

[bjjb99]

Originally posted by Thorpydo
Attempt two failed also..

But I'm learning some everytime.\

Ok, here's what I noticed and possibly an explantion of the problem?

-The 'cracks' arn't really cracks. I'm pretty sure they are rough areas where the bit isn't cutting, just kinda smudging the part.


So it sounds like the flutes of the drill are dragging against the side of the hole you're drilling, and it fits well with the other portions of your description. A bit that's walking around will want to drag along the sides of the hole that's being drilled.


Originally posted by Thorpydo

-As I was cutting, the bit and piece would move around. I can't remeber if they made a circular pattern or if they made a line back and forth. They moved quite a bit. When I wasn't cutting but the drill press was on, the drill wouldn't make the same pattern.


That right there is the clearest indication of a problem. Your part and drill bit shouldn't be dancing about when you're making holes.

To see how stiff the drill bit is, try this... turn off the drill press (duh), wrap the drill bit in a paper towel, and lightly push sideways on the drill bit tip. Does the tip move noticeably when you push sideways? If so, you've got some rigidity issues that need to be worked out before you're going to get to +/- 0.001.


Originally posted by Thorpydo
On both pieces I've used a center drill to mark the center and get the bit going. When I'm setting up the piece to drill, I get the bit and piece lined up pretty well, but not perfect. Maybe this is contributing?


I'd say it's definitely a factor. Being slightly off center is going to cause the drill bit or the part to want to walk around until the hole gets going, and even then the hole itself may not be straight sided.


Originally posted by Thorpydo
Also I've havn't been working my way up with drill sizes. Maybe I'll work my way up on the lathe, and then take it to the drill press for the final 11/16 hole?


Honestly, I haven't had much luck with stepping up in drill sizes. I usually would drill a pilot hole so the center of the drill axis doesn't have to do much cutting, and then I'd drill the hole to the proper size with the appropriately sized drill bit. Every time you change tooling, you risk being slightly out of alignment when you start cutting again. I think you will find that each successively larger drill bit will want to chatter and fight you if you work your way up in drill size, particularly in a hole this deep.


Originally posted by Thorpydo
And also even if the drill bit was smaller it is a MT3 taper shank, and my tailstock is a MT2. I have also have a regular 11/16 chucking bit but that wont fit in my chuck.


Is the shank on the 11/16 chucking bit 11/16 as well, or is it reduced down to 1/2 or so? DeWalt makes an 11/16 diameter general purpose drill bit with a 3/8 diameter shank which might fit your chuck. The flutes are about 3 inches long. Maybe it would fit on your lathe instead of your drill press? Here's the URL if you're interested (apologies if the URL word-wraps):

http://www.dewalt.com/us/products/accessory_category_detail.asp?categoryID=228

I didn't see a price on DeWalt's site, which means you probably have to go through some type of authorized DeWalt sales outlet or something. I can't imagine that it would be more than about $30.00 or so for the bit... might be worth picking one up just to experiment with.

I think if you can find some way to do the whole operation on the lathe, you will probably have better luck. The only problem with a shorter drill bit would be having to flip your part over after you've drilled to the halfway point. But you gain rigidity in both the way your part is held and in the shorter bit length. Just make sure the outer surface has been lightly turned to ensure that the lexan rod is truly circular.

BJJB

[Thorpydo]

I think I've got my solution.

Today I finished the vert tube.. out of polycarbonate. I also started another body hole in some scrap. Looks promising, I hope it will work out.

All I did was mount the piece so that the top is right next to the V block. I originally couldn't do this because the piece would run into the drill press table. Heh, I hung the vise about half-way off the table and then put the V-block in... Looks like a pretty funky setup but it works.

Its still got cracks but these are a different kind and hopefully better =D. They are real small and hopefully will be removed when I ream the hole out.

I finished the sear/linkage for this project, and I'm happy with the results. Since you guys will ask.. It's another custom gun. Its a pump but could easily made semi/electro. Its uses a dump chamber and is semi-similar to a mag in its workings.

I don't think I'm going to be descreate in how it works. I'm pretty sure it's been thought up before. In fact I was talking to someone on AIM that plans on building a VERY similar gun, except that its semi, and not quite how I would do things.

When I'm ready I'll probably make a new post w/ pictures and all that.

[TheJester]

i'm not sure if this has been said, i didn't have time to read all the posts. you may want to try drilling it in steps, that will take less pressure off the drill, making it easier, reducing chatter. also, normally to reduce chatter, if you don't know, is to decreas speed, increase feed. so you may want to turn the RPM's down a tad, and try pushing the drill threw faster. how ever, i would only do this for like a step below you're finished diameter. you said you'll be reaming, and you normally use a fractional size smaller and just ream at the recomended speed (i forget what it for plastics, i know it's slower for plastics, but RPM's are calculated by the formula CSx4/cutting diameter (drill size in this case) where the CS is the cutting speed (90 for steel drills, 300 for carbide). that's for maching steel though, and reaming, you always cut the RPM in 1/2, you'll also want to run the reamer threw nice and slow for a nice finish MAKE SURE YOU USE CUTTING FLUID WHEN REAMING. in terms of cutting fluid, sorry, but i can only speak in terms of steels, but it can at least give you some where to start. hydralic oil works fine, but being that it's lexan i think the oil may coroad the plastic (kinda like gas will styrofoam, but not quite as bad). if you can go to barns and nobels or something, go to the engineering section and look for the "Machinery's Handbook" you don't wanna buy it prolly, it's like 80 bucks, there's a section in there that's all about maching plastics, just read the realivant info right there in the store, and just remember what it says about what you're doing

[Thorpydo]

Ok, Thanks.

I got it working well, but I might still go down and take a look at that book. Sounds good and I've heard it recomended often.

Here's a link to what I'm actually doing with these pieces:
http://www.automags.org/forums/showthread.php?s=&threadid=87469