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hwingo
06-25-2010, 06:04 AM
What is the correct (preferred) way to align a drill bit or milling cutter with holes in a drilling jig? For example, should the jig be first clamped to the milling table and then move the x-y table axis until it “feels like” the drill is entering the hole without interference or should you place the drill into the hole and carefully lower the quill and jig to the table and then clamp the jig to the table before raising the quill?

Second part of this question, "If the jig is fabricated from aluminum (Class 3 anodized surface), what is the best way to protect the holes in the jig thus preserving accuracy for repeated use"?

Harold

beanbag
06-25-2010, 06:15 AM
Proper way:
Use a spinning center finder and touch the inside of the hole at four points.

Less proper way:
Use a non-spinning center finder and poke it into the hole with the quill. Feel the offset of the center finder with your fingernails and move the xy table until the offset goes away. Then rotate the spindle half a turn and repeat, in case there is any runout on the center finder.

Lazy way:
Make sure the drill is not bent. Place your finger against the drill with the lightest possible pressure. Use the quill to poke the drill into the hole and feel if there is any deflection. Then rotate the spindle half a turn and repeat.

No idea on part 2.

oldtiffie
06-25-2010, 06:37 AM
Part/question 2.

Insert (press) a hardened steel sleeve/bush - or at a pinch - unhardened steel.

Pressing in is easiest but making the bush removable/replaceable is better.

What-ever suits - horses for courses.

strokersix
06-25-2010, 07:39 AM
beanbag, pardon my ignorance but please explain the first method with the center finder. I have a center finder set but the only tip I've ever used is the pointy one. Does this method use one of the other tips?

I've always used my Last Word (last chance?) to find hole centers if I needed accuracy. I think I can get within .0005" with it. If there is another method to do it I'd like to know.

ptjw7uk
06-25-2010, 09:01 AM
My take on part 2, If the jig is to be for many uses then make hardened inserts to fit these can then be changed if they get 'too loose' as per dowelling jigs. Inserts can have flange at top with flat so screwin jig plate stops it rotating.
My 2p worth.
On the first I've always centered on the drill then clamped the jig to the table, usually good enough for my level of accuraccy thats why I use ajig.

Peter

hwingo
06-25-2010, 09:13 AM
Part/question 2.

Insert (press) a hardened steel sleeve/bush - or at a pinch - unhardened steel.

Pressing in is easiest but making the bush removable/replaceable is better.

What-ever suits - horses for courses.

Good morning Tiffie,

I have most likely missed something here, or because of brevity I failed to provide sufficient information. Please allow me to provide more information.

I have purchased a rather expensive aluminum jig. This jig has 9 precisely placed holes of varying sizes that are to be used as guides when when drilling into the work piece. I am fearful that the flutes of the drill bits with score, erode, or otherwise alter the guidance holes with use. I think I am hearing you say that I should enlarge the holes of the jig and fabricate hardened steel bushings that can be press fitted into the jig. There are places on the jig with sufficient space which would allow for this but several of the holes are *very* close to each other while two holes are against edges at either end.

Should I expect, that if careful, I will be able to reuse this jig 5 or 6 times before hole distortion occurs due to drill flutes eating away at the sides of the jig holes? I have heard that Class 3 anodized aluminum can be quite hard but I have no idea how much protection this offers.


Harold

Duffy
06-25-2010, 09:26 AM
This is DEFINITLEY an amature's suggestion. First, I assume that this jig is not intended for hundreds of uses. Why not buy a drill blank of the size of the drill you are using? Chuck the blank and use it to align the jig and clamp it down. Then instal a drill and have at it.

hwingo
06-25-2010, 09:26 AM
My take on part 2, If the jig is to be for many uses then make hardened inserts to fit these can then be changed if they get 'too loose' as per dowelling jigs. Inserts can have flange at top with flat so screwin jig plate stops it rotating.
My 2p worth.
On the first I've always centered on the drill then clamped the jig to the table, usually good enough for my level of accuraccy thats why I use ajig.

Peter

Good Morning Peter,

I appreciate your 2p worth of suggestions. One slight inaccuracy is often a multiplying factor causing all sorts of "head scratching conundrums" as one approaches the end of a project. Naturally, I would LOVE to minumize "problem solving" and "last minute modifications". To this end I seek to be as accurate as my machines and instruments will allow.

Harold

hwingo
06-25-2010, 09:30 AM
This is DEFINITLEY an amature's suggestion. First, I assume that this jig is not intended for hundreds of uses. Why not buy a drill blank of the size of the drill you are using? Chuck the blank and use it to align the jig and clamp it down. Then instal a drill and have at it.

I have thought of that and have already ordered drill blanks for use. Unless others have a better way, I think this might be the best alternative.

Thanks for reaffirming my thought process. Make me feel better about my planning.

Harold

AlleyCat
06-25-2010, 09:58 AM
You could grind a point on the drill blanks making them into transfer punches. I have several aluminum drill fixtures I use with punches and with drill bits. Hard bushings are pressed into the fixture and then it's clamped to the part. Sometimes I even use a hand drill to make the holes. The drill bushings were replaced a couple of times in ten years. I've made thousands of parts with this setup.

Glenn Wegman
06-25-2010, 10:26 AM
Secure the part/fixture and use a DTI and sweep the bore to align the spindle over it.

oldtiffie
06-25-2010, 10:45 AM
Good morning Tiffie,

I have most likely missed something here, or because of brevity I failed to provide sufficient information. Please allow me to provide more information.

I have purchased a rather expensive aluminum jig. This jig has 9 precisely placed holes of varying sizes that are to be used as guides when when drilling into the work piece. I am fearful that the flutes of the drill bits with score, erode, or otherwise alter the guidance holes with use. I think I am hearing you say that I should enlarge the holes of the jig and fabricate hardened steel bushings that can be press fitted into the jig. There are places on the jig with sufficient space which would allow for this but several of the holes are *very* close to each other while two holes are against edges at either end.

Should I expect, that if careful, I will be able to reuse this jig 5 or 6 times before hole distortion occurs due to drill flutes eating away at the sides of the jig holes? I have heard that Class 3 anodized aluminum can be quite hard but I have no idea how much protection this offers.


Harold

Harold.

As the holes are so close to each other, I'd offer two solutions which can be used either separately or in combination if needs be.

1.
Make thin-walled sleeves that fit into the existing holes. The sleeves need a hole to suit a smaller drill. Fit the sleeves and use then as guides to drill the smaller hole/s say 1/8">1/4" deep.

Use those holes as "pilots" for the required drills

2.
Use shortened drills such that there is as little/short spirals/flutes left. Use the now smooth(er?)-sided drills to "spot" say 1/8">1/4" deep. Use normal size drills to "finish off". The previous/ly shallower depth holes will act as "pilots".

Frankly, I'd drill, say 1/64">1/32" under-size and finish off with the correct sized drills for greater accuracy.

As the jig is aluminium and to prevent or minimise "galling" - which can not only lead to excessive wear but seizure of the drill/s in the hole/s, I'd suggest slow speeds and lots of good cutting/tapping oil. Keep all drills sharp at all times. Clear swarf continuously as it too can cause galling or seizure in aluminium.

A pic with a ruler for appreciation of scale will assist if possible.

Hasten slowly.

Carld
06-25-2010, 11:13 AM
hwingo, the fact that it's made of aluminum tells me it's a one time use jig. If you run a drill through the hole to drill the part underneath the hole will be enlarged from drill wander/wobble.

Can you make a steel jig like the aluminum jig? If not then you can't drill through the holes and reuse the aluminum jig, it just won't last and remain accurate.

Make a plate to mount the part on that you can clamp to the drill press or mill. Then mount the jig on the part and use a drill blank to align a hole, clamp the plate down, remove the jig and drill the hole with a short screw machine drill or spotting drill and finished as needed. Do each hole as outlined above.

That is the only way you can save the jig for reuse and maintain accurate holes in the jig. Yep, it will take a lot of time but that is what it takes sometimes.

beanbag
06-25-2010, 03:49 PM
beanbag, pardon my ignorance but please explain the first method with the center finder. I have a center finder set but the only tip I've ever used is the pointy one. Does this method use one of the other tips?

I've always used my Last Word (last chance?) to find hole centers if I needed accuracy. I think I can get within .0005" with it. If there is another method to do it I'd like to know.

Poke the pointy end part-way down the hole, approximately near the center. Move left until it touches, then zero DRO. Then move right until it touches, and set the dro to half that value. Now you've found the center in x. Repeat for y.

I use this method for small holes.

beanbag
06-25-2010, 03:52 PM
I am fearful that the flutes of the drill bits with score, erode, or otherwise alter the guidance holes with use.

If you put a little radius at the outer cutting edge of the drill, that will reduce a drill's tendency to score up your jig. It will make your drilled holes a tiny bit smaller, though.

David Powell
06-25-2010, 05:07 PM
Why use a jig at all? From the postings it seems like the job is expected to be done on a mill with a readout. In which case why use a jig at all? Just work out your numbers, find your starting place and go to it. I have quite a lot of little jigs that I use for " Standard, non critical parts" and those get used in the drill press until the holes get worn and I then rebush them or just replace the whole thing. If I had say a one off job 10 pieces with 9 holes each depending on the accuracy needed I might well centre drill in the mill and then freehand drill through on the drill press. The procedure must be geared to the accuracy needed, and it must repeat as well on the last part as the first. Hope this is of interest. David Powell.

darryl
06-25-2010, 09:22 PM
I'm thinking that you use the jig to get the hole positions marked out on the workpiece, then do the job on a drill press.

The accuracy of the hole locations is not going to be great simply by using the jig to guide a drill bit. If that is 'good enough' for the job, then why not select a piece of drill rod the size of the holes in the jig, sharpen a point on it, slightly round the other end, and use that to mark out the workpiece- the jig will live longer, and your drilled holes will likely be better centered if they have a dimple to center the drill bit.

Otherwise, I'm with David on this one- seems more like a job for cnc, or handcranking axis to specific points according to a chart for that job.

Robin R
06-25-2010, 10:13 PM
If you are just going to use the jig for marking out, I'd get a set of transfer punches. They probably don't cost much more than a length of drill rod and you then have a range of sizes for future projects. You can probably find a set for less than these. http://www.leevalley.com/en/wood/page.aspx?p=54892&cat=1,43456

You could also use your alluminum jig to create one in MDF, then use hardened bushes like these to make it last. http://www.leevalley.com/en/wood/page.aspx?cat=1,180&p=40089

David Powell
06-26-2010, 12:09 AM
For garden gate engineering, but often jigs are made to use with Number or letter drills or metric sizes, so you dont often have a transfer punch which is a nice sliding fit in the jig or part you need to match. To top that off, my transfer punch set appears to have had the points ground by a drunken monkey on a bad day( Ok what did I expect for under 10$ new?), Making a specific punch oneself is a grand idea, but can the AVERAGE home shop machinist do a really good job of hardening and sharpening such a beast to make an accurate, sharp and long lived tool, certainly a soft one will do for a few holes but are we talking about a production run here? I like using my( Home brewed) readouts. my parts fit as they should and I do not get angry with myself for taking short cuts and needing oversize or sausage shaped clearance holes. But if I only had my drill press perhaps I would look at it all very differently. Regards David Powell.

Rich Carlstedt
06-26-2010, 01:00 AM
Some basic stuff first
A drill jig properly made has harden inserts installed. These are called drill bushings, and are avilable in all sizes to the .001"

Drill jigs are made to be used on Drill Presses, hence the bushing does the job of allignment and control of the drill bit.

Drill bushings are replaceable in normal situations, as they wear.

A drilling jig made with aluminum holes is a temporary jig and not meant for multiple use. You will loose accuracy after the first hole is drilled.
You are far better off, making custom transfer punches and use them for locating starting holes. Those holes should be drilled in two steps, the first with a small drill the fits completely into the dimple, and the second being the sized drill. Alternatively, pick a common size drill, like 1/8" and make up a bunch of steel flanged bushings, all with a 1/8 " bore and the OD's to fit the holes. Insert them and use the Aluminum plate for starting the holes only.
Then you would drill to size without engaging the jig.

If you insist on drilling in the mill, you must float the part/jig before entering the hole.
You are asking for the impossible, let me explain.
A drill jig holds the location of the cutter
A Mill holds the location of the cutter
You cannot have two masters !
The Jig may help you find locations on a mill (w /DRO) and then you do not need it for subsequent work, but expecting to use a aluminum plate for guiding a cutting operation will surely lead to failure

Rich Carlstedt
Manufacturing Engineer

EddyCurr
06-26-2010, 02:45 AM
If mentioned, I've missed the suggestion that a Blake Co-Ax Indicator (http://www.blakemanufacturing.com/pages/aboutus.html)
or one of its clones (Fowler Centering Indicator ...) could help.

.