Just want to know how daft I am.
|Terry Kirkup||02/10/2020 15:37:22|
66 forum posts
Hello again folks, I seek your advice once more.
I know this is ugly but is it good or bad? And should I get a bigger vise (this one 4"?
70mm of 50mm aluminium bar drilled 22mm (tip of 22mm blacksmith's drill just visible on left). I've made a few of these items previously but used boring tools to dig them out from 13mm drilled holes, so the bar was held in the 4 jaw chuck. Took me absolutely ages. I couldn't stop the lathe juddering or the boring bars (in tailstock 50mm boring tool holder) nodding madly! I did try to balance the chuck with weights, hardly made a difference though.
And one more question to our friendly experts - can I use the same method to open a hole up to 30mm in the same material, drill held by ER32 hex collet block in 3 jaw chuck or is my life in danger?
19113 forum posts
Maybe not ideal but when needs must. I have made up a couple of clamping bars from 1/2 x 1" steel that are drilled to suit the tee slot spacings in the mill and another the lathe's cross slide slots that are good for jobs like this.
I'd just hold the blacksmiths drill in the lathe's 3-jaw chuck and not bother with teh ER block & collet.
|old mart||02/10/2020 15:44:18|
|2201 forum posts|
I think you are lucky to be alive.
What size is your lathe and do you have a four jaw independent chuck?
|617 forum posts|
Main problem you have is there is nothing directly behind the area you are cutting. You are imparting a turning motion on the fixture. Also the clamp studs have a bending force imparted. All bad with such a large intended bore.
Place the part on the angle plate so that the intended hole is above it. Make a strap clamp to hold the part, ideally one either side of the hole. A strip clamp can be a bar with two holes in it spaced as per the tee slots. Ideally as well put a fixed stop against either end of the bar to stop it moving sideways under cut.
If using a vice it would need to be big to have sufficient jaw depth to hold the part in at least one see. My suggestion would be to hold as above rather than in a vice.
3947 forum posts
Once you open the hole out to 20mm or so you can flycut it with a chunky boring bar whirring in the 3 jaw
I have used a 16mm bar to 45mm
Grind up a suitable cutter, will go from 20 to 40mm approx
Grind a 2nd bigger one for a bigger hole
extend the cutter a teeny bit after each pass
When you get it right it makes a nice swooshy noise as it carves a hole through the workpiece and the swarf flies away
Edited By Ady1 on 02/10/2020 15:59:40
|Mick B1||02/10/2020 16:03:38|
|1773 forum posts|
It's nasty for 3 reasons:
i) The clamping nut is unable to act straight onto the washer and clamp across its full diameter. It would be hugely better to add an equivalent thickness of support to the clamp on the opposite side of the stud, so as to level the clamp square to the stud or thereabouts, and even out the force the nut can exert.
ii) The clamps should be as close as possible to the site where machining force will be applied. If the hole shown only just clears the vertical plate, the clamps should be closer to it.
iii) It's also undesirable to sidestress the T-nuts and studs like that. Even if there are no dramatic events, there'll likely be some damage to reduce their future usefulness.
For opening up, I'd use a boring head with light cuts or, failing that, a collet- or chuck-held boring bar with a manually-set toolbit to open up to about 29,6 before using the 30 drill as a reamer. Light cuts, slow feed, and sort out the clamping first.
|Martin Connelly||02/10/2020 16:05:25|
1515 forum posts
It the top stud goes up a little more or the bottom stud goes down a little more you have a loose setup. Never a good idea. Put a support on the opposite side of the studs to keep the clamps level so that there is no way for the studs to go loose. A simple machinists jack (see the one made by Dr_DMJN in this thread Stuart 10V Build Log for a simple design) will allow a good solid clamping action. Alternatively have a metal bar across the workpiece with holes for both the studs.
I agree with old mart, you were very lucky - this time.
|Dave Halford||02/10/2020 16:40:15|
|1017 forum posts|
The clamps are dire, the work is trying to twist away from the drill.
I would mount the angle plate in line with the drill.
Cut a chunk of 1/2" MDF to suit the bolts between the rod and the angle plate.
Use a single clamp plate as Jason suggests to hold it all.
Stop drilling when you see MDF in the swarf
|Henry Brown||02/10/2020 17:27:49|
339 forum posts
If I had to do that, a very non-preferred way for me, as I'd have used my mill. If I had to do it this way I'd have got a suitable piece of square or rectangular bar (that will have negligible bend when clamped) and drilled two holes through to match the pitch of the top an bottom T slots that will take your studding. That would be for a one off though and it sounds like you are doing this on a regular basis. As Jason said needs must sometimes but this is far from ideal and I certainly wouldn't try opening it up to 30mm with a drill.
|Martin Connelly||02/10/2020 19:26:05|
1515 forum posts
Rear support of the clamp bar using a clamping set hex coupler and stud as a simple jack. Keeping the clamp close to level is important to avoid side forces on the stud which will encourage it to go down the gradient and so loosen.
|Howard Lewis||02/10/2020 20:30:56|
|3765 forum posts|
Purely my preferences, but if possible I would hold the work in the 4 jaw, with the drill in a chuck in the tailstock.
This should be the most rigid way of holding the work, and least likely to move under the cutting forces.
The method shown is not the most rigid. Martin Connelly's method is better, if you must, since it provides increased clamping forces.. (Don't like the steeply inclined clamps! )
That's my 2 p
|Robert Butler||02/10/2020 20:37:33|
|165 forum posts|
Not to mention stress on the T slots with possible dire consequences!!!!!!!!!!!!!!!!!! Robert Butler
|Nigel Graham 2||02/10/2020 22:08:02|
|802 forum posts|
I realise your photo is simply to illustrate the method but with respect I would -
- put a nut on the top end of the jacking stud to increase the bearing surface a bit, and avoid the risk of harming the end turn of the thread; and
- put the jack further back so the mechanical advantage is in favour of the jack holding the work-piece rather than vice-versa. (It's about 2:1 against in the picture.)
|Terry Kirkup||02/10/2020 22:56:20|
66 forum posts
Well, I retreat red faced, but fully expected! Thank you all for your input here, I will make better arrangements for the 30mm cut.
And Howard, just one thing. My lathe is Warco WM290V. With the workpiece, in fact any workpiece, mounted to the chuck, there's no way these fairly short blacksmiths drill will reach their target, even with the tailstock at its maximum 80mm extension where anything wobbles at the best of times. The cross slide is just far too wide for that, creating a huge intervening gap, so I guess I'll stay with chuck mounted tools for now. Unless I can hold the drills in the toolpost somehow, a wedge type BXA?
19113 forum posts
That's odd Terry as My 280 allows me to drill right upto the chuck or faceplate. Though no leads screw cover on my early one.
|Tony Pratt 1||03/10/2020 08:29:50|
|1269 forum posts|
I also find that with my Warco 290V you can't get the tailstock close to the work, the DRO fixed to the cross slide RH side makes matters worse, I need to look into that sometime.
|not done it yet||03/10/2020 08:57:09|
|5130 forum posts|
I was aghast at that holding solution! If I were holding something like that, I would acquire, or make, a couple of Vee blocks on which to mount the part, then have a couple of straps to secure the part in position. That would (hopefully allow the machining to be carried out closer to the centre of the holding device and permit cutting through the pats without cutting into the holding kit.
Holding solutions can often take longer to sort out than the actual machining of the article.
|larry phelan 1||03/10/2020 11:19:27|
|867 forum posts|
Delighted to have seen that setup !
And I thought my efforts were bad !
However, I do admire a brave man., but I really think a 4 jaw chuck would be a better idea.
I can just picture that piece taking off at a rates of knots when you start cutting
|Brian Wood||03/10/2020 11:28:03|
|2287 forum posts|
I have another suggestion and that is bolt the 4J chuck to the angle plate and hold the job that way.
I noted that the next hole will be 30 mm diameter which will be significantly more demanding on the workholding needed
|Neil Wyatt||03/10/2020 11:34:09|
18316 forum posts
Sometimes it's needs must as the devil drives...
In which cases light cuts, gentle feeds and an abundance of caution are in order. Think 'what's the worst that could happen'?
In this case poor finish or a broken cutter, I got away with just the first, which didn't really matter as I was just opening up the slots.
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