Forstners

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Brian
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Forstners

Sun Jul 02, 2017 6:43 pm

I'll pose this question here since I'm sure you guys are amongst the only people who will understand what I'm after. I posted on SMC only to recieve an 'oh why does it matter!?! ' Response.

Forstners for drilling at an angle using a machine. I have a Famag bit with a few more en route, but longer term would I be better served using something like the Zobo setup with adjustable center pilot?

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Brian
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Chris Hall
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Re: Forstners

Sun Jul 02, 2017 10:10 pm

I have found that regular Forstners cut quite well on angled surfaces. I'm not sure that a pilot is going to make for much improvement, though it might not hurt either. Presumably you would first drill a hole for the pilot - what keeps that hole from wandering?

Why not take some of your Famags and try drilling some angled holes?

Or are you more worried about putting the hole on a given center mark, when the drill comes in in at an angle such that it's cutting rim contacts the wood before the center? If that is the case, the problem is easily solved using a center point in the drill chuck to align the work to the spindle before drilling with the Forstner.

If you are going to use the mill, you could consider using end mills and a Criterion head with boring bar instead of drills - I can't see how you could get much more accurate and true than with that approach.
durbien
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Re: Forstners

Mon Jul 03, 2017 1:28 am

Aw. I used to work at Criterion. I used to tell everyone I couldn't get a job drawing exciting tools so had to settle for the boring ones.. Yeah.

I didn't stay long, and the company's since ceased to exist - not much call for those tools w CNC about.. Oh well.
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Re: Forstners

Mon Jul 03, 2017 7:39 am

I guess the makes sense that CNC would render boring heads obsolete. It's a good tool all the same. Were you a draughtsman at Criterion then?
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Brian
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Re: Forstners

Mon Jul 03, 2017 7:45 am

Thank you both, glad there are people sympathetic to my type of crazy. I also must have needed a reality check. I plan to use the Famag for the current job but in reading so many tool descriptions I couldn't help but wonder if there is something I'm missing out on in the way of precision.

These are small holes, haven't decided exactly just yet but I'm between 3/8, 11mm and 7/16". I don't realistically expect much deflection but I wanted to be sure that I'm on the right track.
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Chris Hall
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Re: Forstners

Mon Jul 03, 2017 2:33 pm

If the tool holder is slim enough that it doesn't run into the stock on angle (no bigger than an adjustable chuck), I think an end mill might be what I would look to use, so long as the depth of cutting is not more than 1.5" or thereabouts. A 3/8" end mill is going to be significantly stiffer, and therefore less prone to deflection, than the Forstner. Only the cutting end of the Forstner is hardened, while the entire end mill is made of carbide. Both end mill and Forstner can produce a flat-bottomed hole, but the most accurate hole is likely to be made via end mill I would tend to think.
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Brian
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Re: Forstners

Mon Jul 03, 2017 3:31 pm

Good idea, I will go that route instead and save my forstners for some other work.
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Chris Hall
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Re: Forstners

Mon Jul 03, 2017 3:37 pm

If you end up looking to do a 7/16" hole size, then Leigh has a 7/16" up spiral router bit with 2" cutting length - that's the longest I know of in that size.
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Brian
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Re: Forstners

Mon Jul 03, 2017 5:25 pm

Good thing is that the holes are relatively short, only about 1" long so I should be able to cover it with a normal length up cut bit.

Very much appreciate your help on this!
durbien
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Re: Forstners

Tue Jul 04, 2017 7:08 am

Chris Hall wrote:
Mon Jul 03, 2017 7:39 am
I guess the makes sense that CNC would render boring heads obsolete. It's a good tool all the same. Were you a draughtsman at Criterion then?

Yes - the Engineering department then ('90s) was basically only two guys, so they needed the help just doing drawings. They were using CADKEY, so they actually trained me in it. It was really my first real CAD job. They were running three shifts then, cranking out (IMO) a lot of tools - though guys then were talking about how relatively slow it was (with less Aerospace work, apparently). I left when I got my current job, but I still go by the place every now and then. I think they finally liquidated the last of the physical plant and the machinery within the last year or two. It's funny, I still work with several people that used to work there. Insert comment on American manufacturing here, I guess.

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