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Drilling on lathe question

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Forum topic by LeChuck posted 03-11-2013 05:30 PM 862 views 0 times favorited 17 replies Add to Favorites Watch
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LeChuck

418 posts in 1751 days


03-11-2013 05:30 PM

Topic tags/keywords: lathe driliing

Hi folks,

OK, so I have a small Harbor Freight lathe, the smallest one with the electronic variable speed control.

I used it recently to turn the end caps for my workbench handle. That wood was hard. It was my first time ever using a lathe. Anyway, the knobs turned out acceptable in terms of turning despite this not being a fun experience at all, but I did have trouble with one thing and wanted to see if it’s something I was doing wrong, a common issue, a problem with the equipment etc…just to understand how this is supposed to work.

I was using a PSI Barracuda jaw on the lathe to hold the knobs, and I had installed a drill chuck in the tail (also bought from PSI). I wanted to drill a hole into each of the knobs at the center, to receive the tenons from the handle.

In the drill chuck, I installed a 1/2 inch brad point bit. The lathe was going (I tried several different speeds) and I was moving the drill bit in slowly by turning the tail knob by hand, backing out a bit, then going back in.

What would happen is that the wooden knob would actually grab the drill bit and freeze it (motor would stop) and as it was doing that, it would force the screw on the tail stock and actually have enough force to force push the tail back on the cast iron bed even though it was clamped tight and I had to quickly switch the lathe off.

I tried many times at different speeds with similar results. In the end, I had to go to the drill press to drill those holes, which ended up not being totally in the center, and even quite a bit off.

Was I doing it wrong? Was the drill bit too large and I was being too ambitious? Was brad point the wrong type of drill to use? The wood was some African mahogany and it was really hard. Perhaps a super slow speed would have been best as I was getting a lot of burning as well, but I’m not sure that’s the entire issue.

Thanks for any pointers if you have experience with this.

-- David - Tucson, AZ


17 replies so far

View moke's profile

moke

518 posts in 1465 days


#1 posted 03-11-2013 06:10 PM

David,
I drill pens on the lathe only. My holes are obviously smaller, but there are some tricks that make it easier….
1. I always use a starter bit. This bit is just a makes about an 1/8” or smaller hole. I get mine from a machine shop supply here in town but recently saw them at HF…5 sizes for 5.00. That should be great to start.
They act like a center punch sort of. Sometimes longer bits may not be exactly centered ( Like a few thousandths off) and it will then be exaggerated by the spinning of the lathe and the grain and the hole will be oversize.
At the very least, start at 1/4 or even less. The 1/2” bit is more than likely your issue. It is a big bit that can catch in grain.
2. I have never been a fan of bradpoint bits in a lathe. IMHO there are too many points in contact with the product-too much to catch. In fact I have some “fast spiral” bits I use some times, that have a greater point in the center and the material is pulled out faster and more aggressively by the spiral than even a normal bit. At a minimum just use a normal bit.
3. I would not go faster than 1100 to 1200rpms. There is a heat build up inside the piece at any higher speeds.
4. Advance the bit VERY slowly…like 1/8 of a turn every few seconds. Pull the bit out and let it cool every 10 turns or so. When I am doing Polyresin blanks, I often even shoot air down the hole.
5. Take your left hand and hold the drill chuck firmly while with your right turning the tailstock.
6. Grain is very unpredictable. Bits will follow some grain patterns sometimes…you would think not, but it happens more than you think.

All in all I just think you were too aggressive with the bit, maybe the bit feed rate
, and maybe even the RPM speed.
Just my .02
Mike

View shampeon's profile

shampeon

1378 posts in 872 days


#2 posted 03-11-2013 06:17 PM

I agree with Mike. Drilling out with a 1/2” bit is way too aggressive anyway, and especially so with a brad point.

I would probably drill a pilot hole with a small bit and either work my way up with regular non-brad bits. Or maybe the best method would be to drill the 1/2” hole first on the drill press, then take the blank to the lathe and chuck it up to turn the caps round.

-- ian | "You can't stop what's coming. It ain't all waiting on you. That's vanity."

View LeChuck's profile

LeChuck

418 posts in 1751 days


#3 posted 03-11-2013 06:23 PM

I thought about drilling first, but I don’t really see any way that I could have turned the caps so they cold both be round and have the whole centered in the end. Also, I turned both end caps at the same time on a longer spindle that was held by a live center in the tail stock, so I couldn’t have a hole there.

Thanks for the tips both, its very likely to be the bit that was too big, but I was more in a drill press mentality where drilling smaller holes first makes it hard to locate and center the bigger bits. Next time I’ll try with smaller twist bits and see how it goes.

-- David - Tucson, AZ

View shampeon's profile

shampeon

1378 posts in 872 days


#4 posted 03-11-2013 06:31 PM

I think I would turn both individually, after drilling the hole for the handle. Your lathe chuck then holds the caps in the handle hole with the jaws on the inside, and you true up the outside of the caps. Use calipers to make them the same size.

I suppose you could turn the blank to rough size before cutting and drilling for the handle hole, then chuck the caps up to do the final truing.

-- ian | "You can't stop what's coming. It ain't all waiting on you. That's vanity."

View moke's profile

moke

518 posts in 1465 days


#5 posted 03-11-2013 06:33 PM

You could have turned it to size with your live and dead centers, then drilled the holes holding your material in a chuck, then part it off. You could sand the corners off by hand.
Mike

View LeChuck's profile

LeChuck

418 posts in 1751 days


#6 posted 03-11-2013 06:36 PM

This is a good point. I did not think of holding the blanks using the inside of the handle holes. Very good idea for next time.

-- David - Tucson, AZ

View LeChuck's profile

LeChuck

418 posts in 1751 days


#7 posted 03-11-2013 06:39 PM

Mike, what I did was turn both end caps on the same spindle, then part them off, leaving tenons to hold them separately in the chuck. That is when I tried to drill the holes and it went bad. I’ll try both techniques next time, smaller bits on the lathe if I want to drill the holes after turning, or drilling them on the drill press then use that as the base for turning.

-- David - Tucson, AZ

View bondogaposis's profile

bondogaposis

2598 posts in 1040 days


#8 posted 03-11-2013 07:20 PM

I have drilled a lot bigger holes than 1/2” on my lathe w/o a bit of problem. Perhaps the HF motor is a bit wimpy if is stopping completely. Maybe try a forstner bit instead of a brad point or a different bit, maybe it’s dull. I drilled a 1 inch hole using a Forstner bit on this scoop just yesterday in white oak. Make sure the bit is sharp and slow down the lathe. Maybe it is the particular piece of wood you have, try it w/ a scrap of pine just to see if it works on a easier piece of wood. You should be able to do this on the lathe.

-- Bondo Gaposis

View LeChuck's profile

LeChuck

418 posts in 1751 days


#9 posted 03-11-2013 07:27 PM

I don’t think the motor is too wimpy for this as it manages to actually force the tail stock to unscrew and pushes it back on the lathe bed no matter how tight I clamp it down, but I do think the wood is very hard. When I used the same wood for my workbench vise jaws recently, I got a big wood screw completely stuck in it and had to drill it out. So in other words, the wood’s hold on the drill bit is higher than the tailstock’s hold on the lathe bed. If the motor was more powerful than this, I’m afraid something could have broken off or started flying. But it is a small lathe after all.

-- David - Tucson, AZ

View hairy's profile

hairy

2066 posts in 2221 days


#10 posted 03-11-2013 07:34 PM

I usually drill with forstner bits on the lathe. Rule of thumb, the bigger the bit, the slower the speed. I think my biggest is 2 and 1/2”. I usually drill around 200 – 300 rpm regardless of the size. Works for me. If the workpiece is long enough to get a steady rest in there, I will use it. It only takes a few minutes to set up.

Put a piece of wood in your jaws, turn it down to a cylinder the size of the hole you want to drill. Drill a hole in a rough blank the same size. Mount that onto the dowel. Use the tailstock to turn to shape. Remove the tailstock to clean up the end.

-- the last of Barret's Privateers...

View REO's profile

REO

628 posts in 763 days


#11 posted 03-11-2013 08:00 PM

if it is unscrewing then the quill must be turning. The quill should have a dogpoint setscrew in it to keep it from spinning. if its spinning you loose control over feed speed.

View LeChuck's profile

LeChuck

418 posts in 1751 days


#12 posted 03-11-2013 08:04 PM

Yes, the quill spins but if the set screw is locked down, then you cannot advance the bit into the piece by manually turning the tail knob.

-- David - Tucson, AZ

View Ripthorn's profile

Ripthorn

770 posts in 1674 days


#13 posted 03-11-2013 08:29 PM

When I am drilling larger holes, I use lower RPM’s, like 500 or less. You say you have the smallest HF lathe with electronic variable speed, but I went to their site and only see two small ones with manual speed changes. Their lowest RPM is listed as 750 RPM. Do you have one of these lathes, or is it some other model number? Or did you retrofit it with electronic variable speed control?

-- Brian T. - Exact science is not an exact science

View LeChuck's profile

LeChuck

418 posts in 1751 days


#14 posted 03-11-2013 08:32 PM

Ripthorn, it’s the small 8×12 “benchtop” model with variable speed control, 750 to 3200 rpm. Model 95607.

-- David - Tucson, AZ

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Ripthorn

770 posts in 1674 days


#15 posted 03-11-2013 08:38 PM

Interesting. How long have you had it, and do you like it?

-- Brian T. - Exact science is not an exact science

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