Line-boring help

[GarageCNC]

HI Guys, I have a projects coming up where I will need to bore through an iron block and then cut bores in each end to accept bearings. Does have anyone have links to a decent guid on how to set up the lathe for line boring, or is there an alternative?

[RICHARD ZASTROW]

You can perform line boring on a lathe if the lathe can accommodate the workpiece and the stroke required to reach the bores. You can use more than one tool to reach both ends, for example.

Line boring can be performed on a Horizontal Boring Mill as well.

There are also portable boring machines.

"google" line boring and you will find many methods, examples and photos.

Dick Z

[handlewanker]

Hi Garage, it will depend on if'n you can mount the iron blocks on your lathe crosslide or not.

Some lathes have T slots on the crosslide and you can remove the compound slide and then bolt the job to the crosslide top and use packers to bring the job up to centre.

The term line boring means that you rotate the cutter on a boring bar between centres and pass the job along the bar ...the bar does not axially move.... the job does.

For a newbie to turning the line boring method is quite a learning curve, especially when you have to remove the bar to measure the hole diam accurately, and then adjust the tool stick out to bore the hole.

I take it that you are going to have two bores in the block for the bearings with a shoulder at each end for the bearings to butt against, and a smaller diam hole through the block to clear the spindle.

Imediately this suggests that you are using two plain radial ball races, hence the two bores and two shoulders.

Method 1.....An easy way is to bore the small hole right through the block and then bore one end to the bearing finished size for the first bearing.

Next turn the block round and clock the small bore true both radially and as far into the bore as you can get your dial indicator to read in the long ways direction in two planes at right angles to one another.

Provided you get the small bore to run true and the sides of the bore to run true you won't have much problem with bearings not being true to one another.

Another method I have used is to first mill flat two of the outside faces at 90 deg to each other, then you can run a clock along the outside faces to make sure you have the bores in line.

It is important with this method to first line up the block with the two milled faces running axially true, rough drill and bore the small hole first....check the block is still alligned in the two planes, and then finish the first bearing bore diam.....when you do the second side you FIRSTLY align the two milled sides again and then clock the small bore true.....rechecking the allignment of the sides and finally the small bore again.

Line boring is not a method for someone who lacks experience or the equipment.

Method 2....Depending on the size of the block, it is also possible to mount the block on an angle plate attached to the faceplate, (with counterbalances) with the block fastened with clamps and to leave it about 25mm away from the faceplate face....this will allow you to bore both bores in one setting, by back boring the second bore with the boring tool in a conventional boring bar cutting away from the faceplate......and the gap between the block and the faceplate will allow you to get a telescopic gauge in to measure the bore.

If'n you touch the first finished bearing bore diam with the tool point and set your crosslide dial to zero you will have an indication that you are near the finished diam for the second bore.
Ian.

[Geof]

Here is a slight modification/addition to Handlewanker's Method 1:

In the first step do not finish the either bores to size. Leave them 0.015" small.

Turn it around and dial it in as Handlewanker describes but do not worry if you cannot get it "perfect". Now finish both bores to size and face the end so it is perpendicular to the bores.

Now make a stepped mandrel with a diameter that is size for size to the bearing bore with a bit of clearance on the part going part way through the small bore. Machine a 60 degree included taper for a short distance on the end of the smaller diameter and tap a thread in the end.

Make a tapered bushing to fit on the tapered end of the mandrel, with an O.D the same as the small bore in your bearing block. Also make a washer slightly smaller than the small bore with a hole to match the thread in the mandrel. Actually you should make the bushing and washer first so when you make the mandrel you do not need to take it out of the machine.

Now slide the bearing block onto the mandrel, insert the tapered bushing and washer and then bolt them in. The bushing will spread gripping the bearing block and pushing it firmly onto the mandrel.

Now finish the second bearing bore. You are only taking off a small amount so the friction grip on the mandrel will be fine.

This procedure is a bit more involved than Handlewankers but it can give you a more precise end product. If you are doing more than one bearing block this procedure can be faster than tediously dialling the block in for the second bearing bore.

[txcncman]

To be true line boring, once the boring bar and guide bushings in pillow are in place, you clamp your tool holder with cutting tool to the boring bar and without moving the bushings or pillow blocks, your bore out the diameter on one end, and bore the through hole, adjusting the tool as needed to get to the size desired. Then move your tool holder to the other end, facing the opposite direction and bore that end, adjusting the tool as needed to get to the size desired. This is almost impossible to do in a lathe for lack of places to clamp the pillow blocks needed to keep the boring bar in line. It is almost impossible to do this on a vertical mill also. The ideal machine to do true line boring is a horizontal boring mill. You can do a semblance of line boring on other machines, but without the pillow blocks and guide bushings in place to keep the boring bar aligned, you do not have true line boring.

All that said, as long as your hit the numbers needed for size, location, and position (TIR and concentricity), then, it does not really matter how your machine it.

[handlewanker]

Not quite true TX....it is quite easy to line bore in a lathe, I mean truly line bore, provided you can fasten the job to the top of the crosslide, which a number of lathes allow you to do by virtue of the crosslide tee slots.....the crosslide must be locked tightly in position by tightening the gibs.

You must have the boring bar between centres with a single point tool sticking out from one side and you pass the job along the bar by traversing the saddle.....the bar does not move end wise, both bores will be in line and of the same diam....that's line boring...facing the bore shoulders for the bearings is a different matter.

The boring bar between centres in a lathe allows you to remove it to measure the hole, adjust the cut, sharpen the tool, replace the tool etc.....whatever, and replace it without disturbing the job and be back on diam and in line...perfectly.

BTW, the action of boring a deep hole in a block of metal in a vertical mill with the job held in a vice and using a boring head is by virtue of it's action a form of line boring...IE, even though the boring head boring tool is not supported at its end, the job is stationary and the boring bar rotates....the hole will always be the same diam from end to end.

This is where boring a hole in a lathe differs from line boring, where the job is mounted in a four jaw chuck or a faceplate and rotates and the boring bar is stationary...leading to a tapered bore, even though it is round.....no lathe can bore a hole truly parallel with the job rotating and the boring bar stationary....99.99% maybe...but not 100%....line boring will give 100% every time...tool wear disregarded.

I once saw a guy on a horizontal borer who thought he could line bore a hole four feet between holes with a line bar 2" diam and 6 feet long....you should have seen the tool bit jumping up and down in the middle of the bar, even though the end was supported in the tail bearing support.
Ian.

[txcncman]

@wanker - I guess you missed the part where I said, "This is almost impossible to do in a lathe for lack of places to clamp the pillow blocks needed to keep the boring bar in line. It is almost impossible to do this on a vertical mill also." Almost impossible and impossible mean two different things. I will stand by my statement as being 100% true and correct.

[Geof]

.... "This is almost impossible to do in a lathe for lack of places to clamp the pillow blocks needed to keep the boring bar in line....

This may be a correct statement but considering that to line bore on a lathe you do not need pillow blocks you do it between centers as HW describes it correctly doesn't mean much.

[txcncman]

I will still stand by my statement on the grounds that it really all depends on the job. Sure, in most cases, the tailstock would offer adequate support for a line boring operation. But not all. And...if you read the very last line of my post it says, "All that said, as long as your hit the numbers needed for size, location, and position (TIR and concentricity), then, it does not really matter how your machine it." So, someone can pull a sentence or two out of context if they want. I think the message as a whole still has merit.

I have "line bored" each end of a part by attaching it to a 4th axis and then end milled the bore on each end. The results were the same as if I had actually set it up as a true line boring operation.

[handlewanker]

TX, where you would be line boring in a lathe, If'n you really had to go down that path, the fact that you'd have a bar between centres makes it "ever so easy peasy" to do a job mounted on the crosslide.......the crosslide does not have much surface area sideways to actually get ambitious and mount a huge job, but I expect a 10" swing lathe could manage a job with two bores spaced about 300mm (12") apart and that would mean a bar, say 30mm diam, and 600mm long would comfortably fit between centeres and not deflect under load.....this is by no means "near impossible" or anything like it, having done that operation on several occasions.....and the very fact that you can remove the bar to measure the holes makes it extremely easy....amd as Geof said you don't need pillow blocks.

You do need support to the centre of a long bar/small diam when you're on a horizontal borer...been there done that on many occasion....but we're talking about a bar a couple of feet longer than the lathe one.....however, and this is a fact, like it or not....when you place the pillow blocks to support the long bar you actually are deflecting the bar back from the sag it has due to it's length, and so the allignment of your bores is a bit iffy......and I've seen more bores in misallignment due to this factor.....but maybe you have a magic compensation factor you apply?

If'n you don't believe that a bar 10 feet long and 2" diam supported at both ends can sag....welcome to the real world.....if'n you aren't aware of the bar sag that occurs...your holes will all be in the same plane as the sag in the bar....LOL.
Ian.

[txcncman]

Funny how someone can get so obsessed on a detail that they overlook the big picture.

[GarageCNC]

Lol, thanks for the replies, there is a lot of information in here.
I have ordered the iron block, 120 x 120 x 100mm, and I will mount on the cross-slide of a Southbend 9" copy (Smart & Brown Sabel).
I am now struggling to come up with a way to make a tool to bore 2.5" through bore on that small lathe. I am thinking of making the biggest bar I can get through the headstock of the lathe, centres-drilling each end, and then perhaps making a collar to hold the cutter. I am worried about deflection since I can only get 1" through the headstock.
Any ideas on making a bar?