Flat bottom bore on mill

[Justin Beebe at Folsom Tool]

I need to drill or bore a hole on a horizontal mill that has a flat bottom. (No drill point allowed). The hole is .375 diameter 2.559 deep. The material is aluminum 6061. The tolerance is +-.004 on the depth and the diameter. Whats a good way to make this bore with the flat bottom. I was thinking of trying a flat bottom drill but I never used one before. Is this a good approach and if so do I need to rough the bore first then finish with the flat bottom drill? Would using a boreing head be a better option?

 

Thanks

[MotorCityMinion]

+/-.004. Flat bottom drill should do it as a second tool. If location is an issue, C.E.M. with a flat bot would also work good.

[YoDoug®]

http://www.harveytool.com/products/product...26+Counterbores

[dforsythe]

OPTIONS

 

1) SPOT, DRILL , FLAT BTM DRILL

 

2) SPOT, DRILL, PECK OUT THE BTM WITH RELEVED .375 EM

 

IF TIGHT LOCATION +/- .003

 

3) SPOT , DRILL .370 X 1.0 DEEP , .250 STUB EM TO OPEN UP TO .375 X 1.0 DEEP FOR POSITION, DRILL .375, FLAT BTM FLOOR OR PECK WITH .375 EM

 

IF TIGHT LOCATION +/- .001

 

4) SPOT , DRILL .368 X 1.0 DEEP , .250 STUB EM TO OPEN UP TO .368 X 1.0 DEEP FOR POSITION, DRILL .368, BORE TO .376. CLEAN UP FLOOR WITH .375 FLAT BTM DRILL OR .375 EM

[hugh jars]

Watch it with the endmill. Some endmills have quite a lot of "dish". If you plunge a hole it finishes up deeper at the edge of hole than at centre. As MCM says you need a flat bottom cutter. Manufacturers can supply but, over here at least, you do need to ask for it.

[35K chipper]

+1 to Doug,

that's the ones i use in 6061.

 

 

35k

[Dave.L]

I agree with Doug, the Harvey tool will work well but be sure to drill the hole first and just use the Harvey tool to finish the dia and the flat bottom.

 

If you use a 130 or 140 self center drill, you won't need to spot. We only spot for very small drills.

 

If you try this with an endmill, you will get major chatter on the walls.

[Justin Beebe at Folsom Tool]

Thanks for all the replies. The tolerance for the location is +-.002 in the X direction and +-.002 in the Y direction. The tool from Harvey looks good. I'm always pleased with there products. Do they make those in metric. This part also has another bore coming through the other side of the part with a flat bottom that has a diameter of 8.1mm or .319 inches. This one is only 1.102 deep with the same tolerances.

 

Thanks for all the help

[Robert Ouellette]

i personally would helix bore with a 1/4" endmill and call it a day. do it all the time and much faster then spot, drill, interpolate with end mill. just go in there with an end mill and helix bore.

[Dave.L]

quote:

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i personally would helix bore with a 1/4" endmill and call it a day. do it all the time and much faster then spot, drill, interpolate with end mill. just go in there with an end mill and helix bore.

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I find that this does not work so well. More often than not, the chips don't get out of the way.

 

Also, I don't think you will get a flat bottom with a 1/4 endmill in a 3/8 hole. The bottom relief will still show a dish in the middle of the hole. You would need a smaller tool to pass over the center more.

[Mic]

The depth in this case would also be a problem for helical milling. With a 1/4" endmill you would have a length to depth ratio of more than 10xD. This isn't good.

 

Do you have access to EDM?

[Justin Beebe at Folsom Tool]

Mic

 

No EDM.

[Eeyore-nonhuman forum member]

I would drill rough hole first .

0.3 mm less then the target hole height and diameter

then I would contour mill it with end mill 8 mm with ultra short flute length and I would make the end mill rise after every depth to extract chips

in depth settings I would make rough cuts 6 mm and

10 fine cuts with depth 0.3 mm to mill the remnants of the drill cone

s2000 f150

 

Make it all the time

to speed up the process rough bottom drill with end mill or 180 degrees grinned drill

 

HTH

[Josh T™]

I'd Helix Bore it with a 5/16 Flat CEM

[Odell]

Kennametal has some FB drills that I use in allum. that there is no need for pre-drilling or spot drilling. Just move to location and drill. They work great. Page a26 of there innovations/cutting tools 2011 book.

[88Matt]

We have to bore holes all the time. Depending on Ø & depth I will drill or helix bore first but I have to finish with the bore because GDT callouts. Just because positioning is wide open, circularity, cylindricity, straightness, etc. can be tight and not achivable on many mills with helix bore. One part we just finish in ss was approx. 3/8 Ø x 4 deep w/ a step and we c'drilled, drilled, helix bored, fb drilled, and used a special ground bottom cutting reamer with 1000psi thru-spindle coolant to achieve the GDT and surface finish callouts.

[jhjr]

I use k-tool flat bottom drills every day. They work awsome. No predrilling or spot drilling needed. They've held up better for me than kennametal index drills do so were switching all our drills over from kennametal to k tool as they need replaced. Good finish also.

[Justin Beebe at Folsom Tool]

Thanks every on for the help. I ended up drilling the hole to .359 diameter then reaming it to .375 diameter down to the start of the drill point. Then I went in with the flat bottom counterbore tool from Harvey Tool to remove the material left from the drill point. This works very well. Next time I get a part like this I think I will try the flat bottom drills to see if I can save some time.

 

Thanks again

[Verndog]

Spot drill, drill, ream, helix bore the bottom only with 5/16 ext. relieved shank staying .001 off the wall. Way faster then helixing the whole bore, and chips are pulled out with peck drill cycle.

[Colin Gilchrist]

I would do it with two tools. Drill undersized to depth with a Peck Cycle. Then Helix Bore to the start of the drill point with a 5 Degree pitch. Then a separate operation to finish the floor with a 1.5 Degree pitch.

[Dave.L]

No offense to anyone but spot drilling and reaming are a waste in my eyes. If you use a split point-self center drill you don't need a spot drill. And, what is the reamer doing for you? IMO - nothing. Based on your tolerances and locations, both of these are not needed.

[Verndog]

quote:

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No offense to anyone but spot drilling and reaming are a waste in my eyes. If you use a split point-self center drill you don't need a spot drill.

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Depends on how deep the hole is (long drill should be spotted reguardless), depends on how true the drill runs, depends on if you have these tools and the job justifies in qty of parts to buy them, depends on if you want to chamfer the hole. The rule is, there is no rule...common sence must apply.

Reamer is giving you a consistent hole top to bottom without chip swirl that is safer to run (minor drill runnout or dulling does not scrap part).

 

quote:

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I would do it with two tools. Drill undersized to depth with a Peck Cycle. Then Helix Bore to the start of the drill point with a 5 Degree pitch. Then a separate operation to finish the floor with a 1.5 Degree pitch.

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Another effective, fast, common tool method...