4-way toolpost build

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SteveM
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4-way toolpost build

Post by SteveM »

I'm getting closer to finished on a 4-way toolpost for a friend's Atlas 618.
20200508_204637.jpg
I think I'm going to trade him for a haircut, as he is a trained barber, even though that's not his day job.

The toolpost is about 2" square and the slots are 3/8".

Next operation is the holddown screws.

The slot is 3/8" deep so not a lot of room for large screws. I'm not sure if 10-32's will be enough to hold a toolbit.

The toolpost is intended to be used with 1/4", 5/16" and 3/8" tool bits (probably mostly the two smaller sizes).

I was thinking that I could use 1/4" screws and set them back in the slot so that they would clamp down centered on 1/4" bits rather than on the outside edge. The fact that they would be clamping 3/8" bits on the inner half is probably not a problem as the toolbit is pretty wide. Also, if I center the screws in the slot, there's not a lot of meat between the screw and the outside edge.

As to threads, should I go for 1/4-20 to get stronger threads, or 1/4-28 for more clamping force?

The nut will have a nick made in the underside of the threads like they do on T-nuts to keep the screw from going thru. I will take a bolt, screw it in down to the nick then loctite it. The top of the bolt will have the thread cut off and the shank threaded at the top. Then I will either use a plain nut and washer or make a nut with a handle. That way the threading is done at the top and not at the bottom.

Let me know what you think.

Steve
whateg0
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Re: 4-way toolpost build

Post by whateg0 »

I would think that 1/4" -20 would be fine. The threads aren't necessarily stronger just because they are bigger. If 1/4"-28 threads were weaker, you wouldn't be able to apply more clamping force. I would also consider either square head bolts or at least SHCS instead of set screws. Set screws limit you in hex key size so you won't be able to really apply much clamping force anyway. Also, it doesn't take a ton of force to keep the toolbit in place.

As long as you cut the hold-down bolt short enough, it won't protrude past the nut, or better yet, make the bolt go in the compound and put the nut on top. The reason that it's a problem on a mill table is that the studs can spin on both ends. So, it can come out the nut on top or it can go out the t-nut on the bottom. The staked hole on the t-nut forces the stud to stop there and tighten at the top end.

Dave
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Harold_V
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Re: 4-way toolpost build

Post by Harold_V »

If it matters, I have a small fly cutter (about 1½" diameter) that has 10-32 set screws. I use only two of them and have no issues with restraining the tool, which is 3/8' square. I'm known to take serious cuts (in aluminum) and to operate the fly cutter @ 4,200 rpm. I think the fly cutter is made of mild steel, with the threads having served adequately for many years.

Trade for a haircut, eh? I wear my hair long, often beyond my collar. Most folks would think I needed a haircut right after I'd had one. I get it cut only when it bugs me, and that's rarely more than twice per year. If the virus thing doesn't get resolved, I fully intend to use a guide on some electric clippers I have and have my wife give me a buzz cut. That should buy me a year or more.

H

Edit:
Socket sets tend to break out around the hex. That's especially true if they project above the surface. Keep that in mind when you make your selection.
Wise people talk because they have something to say. Fools talk because they have to say something.
RMinMN
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Re: 4-way toolpost build

Post by RMinMN »

If your friend is taking such deep cuts on that Atlas 618 that 10-24 socket head cap screws won't hold the cutter bit, I want to be there to watch. The bit should not extend far beyond the end of the holder for rigidity which then puts little strain on the screws securing it. It does need 2 screws, one to hold the vertical forces and one to keep it from rotating.
John Hasler
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Re: 4-way toolpost build

Post by John Hasler »

I have a toolpost very much like that on my Logan with 10-24 socket head cap screws. It's been working fine for years.
earlgo
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Location: NE Ohio

Re: 4-way toolpost build

Post by earlgo »

Steve:
This is the tool block that I use on the Atlas 12" and it uses 1/4-20unc set screws for clamping. I made the slots 3/8 deep by 1/2" wide so there could be a clamping shim on top of the tool bit so the bit doesn't move when the screws are tightened. No problems have been found in the 10 or so years since this was made.
tool block
tool block
(The drawing says 2015, but it came after the block was made and I retired.)
JMHO
earlgo
Before you do anything, you must do something else first. - Washington's principle.
earlgo
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Re: 4-way toolpost build

Post by earlgo »

Steve, I forgot to mention the obvious. Make the slot in the tool holder low enough so that the largest bit to be used does not have to be ground down on the top to reach the center height. Not a problem with 1/4 " or 5/16" bits, but easy to do with 3/8" bits.
Just a heads up.
--earlgo
Before you do anything, you must do something else first. - Washington's principle.
SteveM
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Re: 4-way toolpost build

Post by SteveM »

I'm going to go with 1/4-20 socket head cap screws. If I can find square head ones later, I can always swap them.

The 1/4-20 will give more surface area so that I can be sure it will be clamping on the bit whether I am using 1/4", 5/16" or 3/8". He will need shims for the smaller tools to get them up to the correct height.

I'm going to mount them slightly inboard to be sure they can get some bite on a 1/4" toolbit. They should easily be able to grab a larger bit.

I figured the bolt pattern I should use is this:
20200509_140646.jpg
This lets me use 2 screws for the toolbit on each side with the front screw close to the corner for better support. It also leaves more meat on the outboard side of the screw.

This way, if he uses bits short enough, he can have four turning bits mounted at once. If he needs to have a boring bar mounted, he would be limited to 2 turning tools (or he might just have to swap out the boring bar if it gets in the way of turning).

Right now, I just have a 3/8-24 nut on there and he can turn it with a wrench. Later, we might make a taller nut with a handle.

Let me know what you think of the bolt pattern and if you have any suggestions.

Steve
whateg0
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Re: 4-way toolpost build

Post by whateg0 »

Why not space the clamping bolts evenly?
SteveM
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Re: 4-way toolpost build

Post by SteveM »

whateg0 wrote: Sat May 09, 2020 1:41 pm Why not space the clamping bolts evenly?
So that each bit will have two screws on it spaced as far apart as they can be.

The red outlines show the location of each toolbit:
20200509_140646 - Copy.jpg
Each has a screw right at the front close to the action and then one as far back as possible.

Maybe I should move the rear screw up 1/4" or so to account for the tool getting shorter from resharpening
earlgo wrote: Sat May 09, 2020 12:59 pm Steve, I forgot to mention the obvious. Make the slot in the tool holder low enough so that the largest bit to be used does not have to be ground down on the top to reach the center height. Not a problem with 1/4 " or 5/16" bits, but easy to do with 3/8" bits.
I don't have the lathe here, but the top of the groove was measured to be good for 5/16" tools, if I remember correctly, and you would have to shim a 1/4" tool. I don't really see him using 3/8" bits, but he does have the ability if needed, although he would have to check the height.

I'm going to make him a bunch of shims, as there is no rocker to adjust the height.

Steve
whateg0
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Re: 4-way toolpost build

Post by whateg0 »

They don't need to be spaced far apart. Sure it's nice, but on my Aloris-style holders the tools are often short enough or I have them extended far enough that only the front two screws are holding it, especially boring bars. Which, btw, would only have two closely spaced screws holding them in that arrangement anyway.
armscor 1
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Location: Philippines

Re: 4-way toolpost build

Post by armscor 1 »

I prefer square headed bolts, socket head tend to fill with chips, especially machining brass.
I have this problem with the compound attaching allen head bolts filling up with chips, have to regularly clean them out with compressed air, annoying.
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