Maurits van Dueren | 21/06/2023 13:28:20 |
22 forum posts 2 photos | So I have a small Myford lathe and am a beginner. I am trying to make a groove (but I ran into the same in the past when doing cutoffs). My problem is, once the blade makes contact, it wants to "dig in" to such an extent I can feel the backlash of my handles go slack. It literally pulls the insert, blade, carriage, to the other side of the spindle slack. Meaning it tries cutting too deep and starts to chatter horribly. In fact, if I do not start 'pulling" on the slack instead, it digs in so deep it stalls. I must be doing something wrong. Please advise
Setup: I have inserts tooling (I am not setup to grind HSS) on a small 0XA 250-000 quick tool post and I am trying to make a 5x5mm groove in a 46mm diameter cilinder I feel no slop anywhere (other then the wheel backlash), in fact I turned on the gibs a little on the tight side to make sure (I have to works the wheels a little) I am thinking maybe I have my approach angles wrong, but it is a pre-made cutoff tool in a 250-001 holder. I notice the dedicated 250-007 cutoff holder is slanted slightly up, but so is the insert in my insert holder, so that should be the same. I have the height such that it is on centerline. But I now wonder, should it be slightly higher to avoid it biting in? Or should I somehow counter the slant that is build into the insert holder?
Any suggestions
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JasonB | 21/06/2023 13:30:48 |
![]() 25215 forum posts 3105 photos 1 articles | Are you trying to cut the 5mm width in one go? in other words is it a 5mm wide insert. |
Maurits van Dueren | 21/06/2023 13:35:22 |
22 forum posts 2 photos | Heavens no. It is a tiny Myford. No, it is a 2mm wide insert. |
Nigel Graham 2 | 21/06/2023 14:00:31 |
3293 forum posts 112 photos | I'd go with Jason's suggestion irrespective of tool width. Also, slight angular misalignment? I square my parting-tool holders, whether HSS or carbide (I use both), to the face of the chuck. Grinding HSS tools on a normal bench-grinder is not too difficult, with some practice, though it helps if you replace the usual tool-rest with a larger, adjustable table. |
Ady1 | 21/06/2023 14:02:13 |
![]() 6137 forum posts 893 photos | Cutting upside down is the easy solution When parting off every tiny tiny improvement makes a big difference, so think carefully about what is going on |
Hopper | 21/06/2023 14:04:28 |
![]() 7881 forum posts 397 photos | What RPM are you using? Sounds suspicious that your tool holder is holding the blade at an angle, then the insert is also angled in the blade. Those type of cut off tool is usually held level, so the insert provides the back rake angle. The tool holder is probably designed to hold a straight HSS type of blade at a slight angle. So you probably have double the angle required. Which would cause it to dig in as you describe. Pics of your set up would help see what is going on. Also, lock the carriage and the topslide while parting off or grooving. Run the RPM a bit lower than you would for turning the same diameter. Low speed of 200rpm on a Myford should be ok if all else is well with carbide tooling. And keep plenty of oil, any kind of oil, on the job as you go. Dribble it on from an oil can. Setting the parting tool a bit below centre can help alleviate dig-ins too. Don't set it above. It will rub and can then suddenly grab if you put more pressure on it to make it cut.. I use an inverted rear parting tool in the Myford with good success, but opinions vary on that. You should be able to get the conventional style insert tool to work ok, certainly better than what you are experiencing.
Edited By Hopper on 21/06/2023 14:08:41 |
Maurits van Dueren | 21/06/2023 14:09:11 |
22 forum posts 2 photos | Sorry, cutting upside down? You mean coming in from the back, or with the chuck spinning in reverse? The latter seems like a really bad idea on a chuck that is only held by it's right hand side threads and no key.
I did indeed quare my tool holder against the chuck
So if I would grind HSS, what would be the angles?
As to "go with Jason's suggestion". Maybe I am misinterpreting, but did he make a suggestion?
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Andrew Johnston | 21/06/2023 14:17:46 |
![]() 7061 forum posts 719 photos | Are you using a carbide parting off insert? If so, they are useless for grooving in my experience as they chatter badly if you don't keep the feedrate up. Which is not ideal for sneaking up on the depth of a groove. As a parting off tool they are fine, procvided you keep the feedrate going, a minimum of 4 thou per rev and preferably rather higher. For cutting grooves I use home ground HSS tools as they allow you to sneak up on a dimension without chatter and leave a good finish. Buy a bench grinder and some HSS tool blanks. Andrew |
John Hinkley | 21/06/2023 14:46:57 |
![]() 1545 forum posts 484 photos | Maurits, How much does the tool protrude from the toolholder? Too much and the tool will waggle about like a waggly thing and dig-ins will follow. As you are using a 250-000 QCTP tool holder, you could invest in an HSS cut-off blade such as This one from ArcEuroTrade. It has the top relief already ground into it and will presumably fit straight into your toolholder. As has been said, use lubrication, slowish speed and steady infeed. John
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JasonB | 21/06/2023 14:54:31 |
![]() 25215 forum posts 3105 photos 1 articles | Rather depends on the Insert, I regularly groove with my Mini-thin inserts and sometimes with a MGEH grooving tool but if it is a GTN style parting insert the Myford may not like it unless it is a sharper one intended for nonferrous metal though many get on OK with similar inserts in the "Greenwood" type holder I did not make a suggestion. Just asked for a bit more detail. Edited By JasonB on 21/06/2023 14:55:34 |
Speedy Builder5 | 21/06/2023 15:23:31 |
2878 forum posts 248 photos | Tighten your cross slide gibs a bit more - the screws on the right hand side (usually). |
Howard Lewis | 21/06/2023 16:01:33 |
7227 forum posts 21 photos | As advised, tighten the gib screws. Minimal play in all areas is rhe secret. If the tool has no top rale, it is less likely to dig in. The tool edge should be sharp, on the centreline and square to the tool, and to the lathe axis. An angled cutting edge produces swarf which is wider thann the cut, and likely to jam. Best of all, is to fit a rear toolpost amd mount the tool imverted.. (In that way the swarf falls away asnd is mless likely to clog the cut. ) Feed should be slow, about 0.002" (0.050 mm ) per rev. DON'T rush, and err on the side of low rather than high speed. HTH Howard |
not done it yet | 21/06/2023 17:15:05 |
7517 forum posts 20 photos | You may not ‘feel’ any slop. But we should be talking ‘rigidity’. If the set-up is not as rigid as possible, trouble will arise when parting off (as you say in your post). A groove is nothing different to parting-off, really - just not as deep! Obviously tool condition can be a factor but if that is OK, then you likely have too much machine wear, or too much overhang. QCTPs are not always the best option for small, worn machines! I never really used the silly, angled parting-off tool holder I bought (as part of a ‘special offer’ when buying several holders with the tool post). Rubbish design, as far as I am concerned - the centre height changes every time the cutter is extended, or retracted, in the holder. Cutting from the rear is far better than struggling from the front - every day of the week! Are you using any cutting aid? It needs it - and continuously - IMO. |
Howard Lewis | 21/06/2023 17:57:03 |
7227 forum posts 21 photos | Additionally, I have rigged up a bottle of soluble oil, above the lathe, with a needle valve to provide a steady drip ontom the HSS parting blade in the rear toolpost. This works so well that I very often use power feed to part off! Keep the rpm low. Chatter usually means that bthe speed is too high. Again, rigidity, zero top rake on a sharp tool, and a slow steady feed, preferably mounted inverted in a rear toolpost, would be my recommendations. Howard |
Maurits van Dueren | 21/06/2023 18:20:51 |
22 forum posts 2 photos | Thanks all. So parting was always struggle, but this 46mm part/groove is just proving too much. What really upsets me is this tendency to pull the blade into the workpiece. It even does this on smaller diameters, closer to the chuck. It is very unsettling. I guess I need to pause this project, and first do another one I was already considering: Making a post directly on the crossslide, without the topslide. And by the sounds of it, two of them Anyone has some nice ready made, field tested, plans for a myford?
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Howard Lewis | 21/06/2023 18:29:42 |
7227 forum posts 21 photos | Holding the parting blade in a separate tool holder (Explore the "Gibraltar" toolpost! ) will be more rigid that a QCTP which has an overhange, and several interfaces, each of which will lessen rigidity. If you are going to make a toolpost specifically for parting off, why not make it a rear post, holding the blade square to the lathe axis, with zero top rake, and exactly on centre height? A steady drip feed of soluble oil onto the blade will improve matters even further. My parting blade is 2.38 mm (3/32" ) wide, and is always used inverted.. Howard |
Howard Lewis | 21/06/2023 18:34:35 |
7227 forum posts 21 photos | If you look in L H Sparey "The Amateur's Lathe" or G H Thomas' "The Model Engineer's Wortkshop Manual" you will find designs to fit on the Myford 7 Series. Howard |
Maurits van Dueren | 21/06/2023 18:59:17 |
22 forum posts 2 photos | So how high is your blade? If any potential rear holder is dedicated, it may as well hold a tall blade. So like 3/4" instead of 1/2" (20mm in stead of 12mm) Or at least, I suspect such would also work benificial?
BTW: If I have a dedicated holder, mounted directly on the topslide, would there still be an advantage mounting it in the rear? Or is that merely a habit, so you need to remove it not quite as often (only when it is in the way)
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DiogenesII | 21/06/2023 20:27:59 |
859 forum posts 268 photos | If you mount it at the back with the tool upside down, and run the lathe forward as normal, you are pulling the tool through the work towards you while the rotation is trying to push it up and out - you will see that this is a much better strategy than trying to push it with a screw, whilst the rotation is trying to drag it in and under.. .. .. especially if your lathe is not so young anymore.. Because the tool will be mounted upside down with the tip on centreline, there is no limit to blade depth other than what you can find to hold the desired width of insert. All you really need is a substantial lump of steel or iron to hold a blade in the right position, firmly, at the back of the cross slide.. Edited By DiogenesII on 21/06/2023 20:29:53 |
John Haine | 21/06/2023 20:32:55 |
5563 forum posts 322 photos | What rpm? |
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