New member and need to drill some big-ish holes

[snowkilts]

Hello everyone, I am new to the forum and looking for some direction.

I have a Shoptask 3-in-1, 17" swing (8" over carriage), 20" bed. Unfortunately I have not used it very much, but I have a project now that I am very interested in. I also have some work experience with machining, mostly from the engineering side. This is somewhat helpful, but obviously leaves me a long way from being a machinist.

I am making some parts for my bagpipes (don't laugh! ). The material is delrin rod, 1-1/2" diameter, 6 to 9 inches long. I need to drill a hole through the rod around 7/8" diameter, but could be a bit larger or smaller.

My first thought is to grind an edge onto a piece of drill rod, but I can't seem to find a good way to hold it. All the holders I'm finding are either too small for a 7/8 rod, or too big for my machine. Can someone point me to some sort of inexpensive v-blocks or something that I could use to clamp a drill onto my carriage, with the ability to adjust to the work height with shims or a wedge or something?

I'm also trying to come up with something clever and cheap to use as a follower rest.

I've been googling till I'm blue in the face, but I have the feeling I'm asking the wrong questions...

Thanks!

-- Jon

[jutz]

I'm not at all sure I understand what you are trying to do. If you just need to drill a 7/8" hole down the length of the rod, I recommend purchasing a spade type wood boring bit and using that in the tail stock. Those are my drill of preference for most plastics.

[snowkilts]

Thanks, that's pretty much what I was looking for. I wouldn't have thought a spade drill would hold up, but I'll give it a try.

I'd been looking at this, where the guy is using a gun drill with compressed air to evacuate the chips.

[Harold_V]

I've not tried a wood type spade drill for plastics, but evacuating chips shouldn't be an issue. The shank diameter is so small that there is adequate room for the chips to easily move. Drilling horizontally encourages evacuation.

If you drill in the vertical position, you may have to retract the drill occasionally, but I think you'll be pleasantly surprised to find that the chips aren't much of a problem. That might not be true if you had to drill much deeper, however.

Harold

[david5605]

Why not just chuck a regular twist drill in the tailstock and drill the thing from both ends?

[Jose Rivera]

Why not just chuck a regular twist drill in the tailstock and drill the thing from both ends?

That's what I would do.

Unless having enough OD to make the hole concentric to the OD by machining it to finish, the chances of getting a crooked holed that has been drilled deep are at least 90%.

The best way is to drill smaller some two inches deep or more, then with a boring bar bring the hole to the correct spade drill size, then go from there.

Having a starter hole that is perfectly concentric is the key to drilling deep holes or trepanning.

[jutz]

The spade bits designed for wood working have a brad point which does a good job of staying on center and are only sharpened at the front, so they have a lot less tendency to wander than standard twist drills. They have a lot less surface in contact with the plastic so they don't heat the plastic up as much as standard twist drills. The cutting edges have very little rake (as recommended by most plastics manufacturers) so they don't tend to grab. They can drill fairly large holes in one pass (no pilot drilling necessary). I have drilled 3/4" holes 12" deep in delrin which were straight and non-tapered within less than 0.001".

They're also a whole lot less expensive than twist drills in the large sizes and available with very long shafts.

When I drill plastic with one, I start feeding very slowly to let the brad point find center. Once the outer points of the bit start cutting, I feed fast enough to peel off a continuous ribbon from each cutting edge and back the bit out of the hole whenever the ribbon starts to tangle around the part; sometimes it doesn't tangle at all and I can run the drill straight through.

Yes, a standard twist drill can do the job (and I used to use them) but I highly recommend trying spade type wood bits for plastics.

[snowkilts]

Lots of good info here, thanks. I got a 7/8 spade drill and will give it a try.

A couple other questions that hopefully are not too dumb.

I need to bore the hole a bit larger that 7/8". I can't seem to find a long (12") smaller diameter (1/2" or so) boring bar. Any reason I can't make one? Maybe cut a slot in a piece of drill rod and braze in a piece of something hard, like an old file, that I can grind an edge on?

Also when drilling with the tailstock, my machine has only about an inch of travel. I will have to loosen the gibs, move the tailstock, then drill the next inch. Is this typical, or am I missing something?

Thanks!

[Harold_V]

I need to bore the hole a bit larger that 7/8". I can't seem to find a long (12") smaller diameter (1/2" or so) boring bar. Any reason I can't make one?

You can make one, but if you intend to bore 12" deep, I expect you won't achieve success. By the time you've extended a bar six times its diameter, it isn't very rigid. Chatter is a serious problem, as is chip evacuation.

Maybe cut a slot in a piece of drill rod and braze in a piece of something hard, like an old file, that I can grind an edge on?

The idea will work with HSS, but not with a file shard. They are not typically made of HSS, so any heating will destroy the heat treat of the file. Once you've softened it by brazing, it would be difficult to achieve hardness again. By sharp contrast, you can attach HSS with no observable loss of performance. Just don't quench after doing the attachment. Allow it to cool in air to room temperature.

You do have one option that might work to your advantage, but it's not cheap. A solid carbide boring bar is far more rigid than anything made of steel, so it can be extended to greater depths with reasonable results.

Also when drilling with the tailstock, my machine has only about an inch of travel. I will have to loosen the gibs, move the tailstock, then drill the next inch. Is this typical, or am I missing something?

If you have a small machine that has limited travel, how you described the operation is what you have at your disposal.

I do have a question about your terminology, however. You mentioned loosening gibs. I expect that what you're really saying is that you loosen the tailstock locking device. Tailstocks don't normally have a gib. A gib is typically the adjustable member of an assembly that insures you can achieve a proper sliding fit. While it, too, can function as a lock, it generally is not intended to do so.

Hope some of this helps.

Harold

[snowkilts]

Thanks for the response Harold. Perhaps I'm asking the wrong question. Assuming I am successful in drilling a 7/8" hole through the center of my 1-1/2" delrin rod with a spade drill, what is the best way to make the hole a little bigger? Maybe a 32nd or so.

As far as the gib issue, sorry if I am using the wrong terminology. There is a little piece of metal, maybe 1/4" thick, between the tailstock casting and the front way. I have been calling this a gib. There are two set screws which I assume are used to take up wear. The tailstock is a two piece assembly, with an adjustment between the top and bottom piece to compensate the tail for gib adjustment.

In between the two set screws is another screw with a handle on it which is used to lock the tailstock into position. It appears to just jam the gib further into the ways. This can sort of be seen here: shoptask. Click on History and scroll down to the Shoptask 1720XMTC; that's the machine I have.

Cheers,

-- Jon

[Harold_V]

Thanks for the response Harold. Perhaps I'm asking the wrong question. Assuming I am successful in drilling a 7/8" hole through the center of my 1-1/2" delrin rod with a spade drill, what is the best way to make the hole a little bigger? Maybe a 32nd or so.

I think you and I should have a little talk about what your actual objective is.

Several years ago, when I was living in Utah, I was associated with the Salt Lake Scots Pipe Band. The pipe major kept talking about building an adjustable blow pipe, so I offered to make them.

My choice of material for the body and stock was black Delrin. The telescoping member was made of 5/8" diameter stainless tubing. Projecting mount was made of natural ABS, which blends nicely with old ivory. The telescoping stainless tube required that I bore the Delrin to a close fit.

Now comes my caution. Delrin is very active when machined. There's considerable stress in the material, which is relieved as you remove any part of the piece, be it the bore or the OD. I turned what was, for all practical purposes, a fully combed body. Between drilling and turning, I found the material would move as much as 1/8", so for the first time in my many years in the shop, I found myself roughing, semi-finishing, then finishing all diameters in order to remove the resulting errors.

To bore the blow pipe, I used a ½" solid carbide boring bar and had no problems. The bar uses inserts, and has positive rake. Depth of the bore was 8½", Luckily, with a carbide bar, the tough limits that are normal for boring metals didn't seem to apply.

Unless you have something you consider proprietary, if you're willing to share a sketch, maybe I can give you some pointers that will keep you out of trouble.

As far as the gib issue, sorry if I am using the wrong terminology. There is a little piece of metal, maybe 1/4" thick, between the tailstock casting and the front way. I have been calling this a gib. There are two set screws which I assume are used to take up wear. The tailstock is a two piece assembly, with an adjustment between the top and bottom piece to compensate the tail for gib adjustment.

In between the two set screws is another screw with a handle on it which is used to lock the tailstock into position. It appears to just jam the gib further into the ways. This can sort of be seen here: shoptask. Click on History and scroll down to the Shoptask 1720XMTC; that's the machine I have.

I took a look at the picture, but it wasn't conclusive, at least not for me. My comments about no gibs on tailstocks is based on my years of experience running industrially rated machine tools. I'm woefully lacking in knowledge where the home type machines are concerned. Indications are that I could well be wrong in my assessment. Do understand that I'm not trying to give you a bad time--just trying to make sure we're on the same page.

Tailstocks normally have a pair of set screws that oppose one another, which are used for adjusting set-over. That's how taper is eliminated, or how shallow tapers are generated. The screws you mentioned may or may not be related to that function. Sorry, I simply don't know in this instance.

Harold

[snowkilts]

Several years ago, when I was living in Utah, I was associated with the Salt Lake Scots Pipe Band. The pipe major kept talking about building an adjustable blow pipe, so I offered to make them.

I'm delighted to find someone on this forum involved in the piping world! What did you do with the band?

Anyway the project I'm working on is top secret, but I'm sure you won't tell anyone. I am making a new type of drone stock. (For others who may read this, the stock is a 6" or so long cylindrical piece of wood or plastic which is tied to the bag on bagpipe. It is drilled through and sized to accept the remaining pieces of the drone. Parts of a bagpipe)

I don't have a sketch, but what I'm trying to do is make a tenor drone stock with a brass tube inserted in it. I want the tube to be suspended in the delrin stock, not touching it, held in by threads at one end. I have some 7/8" brass tube, on one end of which I have soldered a piece of 1" brass tube about 1-1/4" long. I plan to cut threads on this, and screw them into mating threads on the delrin piece.

I recently spoke to a friend who is an instrument repair guy, and he says the way he does stuff like this is just use a drill for the initial hole through the delrin, then size it with a taper shank reamer held in the tailstock. I think I will give this a try with my spade drill and a 29/32" reamer. I will then need to bore out an inch or so of the delrin piece to the pre-thread diameter and tap it. How does this sound?

-- Jon