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Options for replacing 0.01" teflon sheet on HLV-H carriage

jz79

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Mar 21, 2017
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Latvia
I was googling about the subject but see only old posts and no real definitive solutions.

As the topic name suggests, I have a need to replace the teflon sheet under the HLV-H carriage, the dovetail piece looks ok, but the top is scored and around 30% of it has delaminated already and the rest looks like it wants to come off, I see some corrosion of the steel under delaminated portions, so I want to replace the whole thing.

I measured the sheet to be aprox. 0,3mm (0.01"), and the sheets themselves seem to be quite cheap, but then there is the question of gluing it to the steel, I see that there is a Permabond TA4610 (datasheet) adhesive that supposedly can adhere to PTFE, and there is even adhesive backed sheet available (waiting to get info about the adhesive from the seller).

Has anyone here done this with sheets this thin and is willing to share details? With the Permabond the plan was to do few test runs, spread it out using a fine comb working in one direction (miniature version of the sort masons use when they lay tile), do few tests to see how big the comb notches need to be to achieve near 100% glue contact with PTFE yet keep glue thickness to minimum.

I know about the Turcite and Rulon, but those are thicker, and I don't want to do any machining on the carriage, that would be the last resort if the 0.01" PTFE won't stick.

Before anyone asks, the dovetail itself is also quite scored, but I know of no grinding shops in 1000km radius that I would trust regrinding it, so for now it will stay as it is, the wear in the middle is minimal (when measured with mic, to the peaks of score marks), only 0.015mm dip (0.0006"), so the new teflon sheet would work as a temporary measure to get the machine operational and prevent more damage (it will see light use, no production, and no real precision required of it either, for now at least).
 
Gluing a material with one of the lowest coefficients of friction, tricky :)

I found this video if it helps, looking at how much he bends the plate the bonding looks strong:

YouTube

I've seen this used successfully to bond PTFE to astronomy telescope mount slides but there not under the same kind of load
 
I was googling about the subject but see only old posts and no real definitive solutions.

As the topic name suggests, I have a need to replace the teflon sheet under the HLV-H carriage, the dovetail piece looks ok, but the top is scored and around 30% of it has delaminated already and the rest looks like it wants to come off, I see some corrosion of the steel under delaminated portions, so I want to replace the whole thing.

I measured the sheet to be aprox. 0,3mm (0.01"), and the sheets themselves seem to be quite cheap, but then there is the question of gluing it to the steel, I see that there is a Permabond TA4610 (datasheet) adhesive that supposedly can adhere to PTFE, and there is even adhesive backed sheet available (waiting to get info about the adhesive from the seller).

Has anyone here done this with sheets this thin and is willing to share details? With the Permabond the plan was to do few test runs, spread it out using a fine comb working in one direction (miniature version of the sort masons use when they lay tile), do few tests to see how big the comb notches need to be to achieve near 100% glue contact with PTFE yet keep glue thickness to minimum.

I know about the Turcite and Rulon, but those are thicker, and I don't want to do any machining on the carriage, that would be the last resort if the 0.01" PTFE won't stick.

Before anyone asks, the dovetail itself is also quite scored, but I know of no grinding shops in 1000km radius that I would trust regrinding it, so for now it will stay as it is, the wear in the middle is minimal (when measured with mic, to the peaks of score marks), only 0.015mm dip (0.0006"), so the new teflon sheet would work as a temporary measure to get the machine operational and prevent more damage (it will see light use, no production, and no real precision required of it either, for now at least).

.
turcite is glued on then machined. it can start much thicker but after machining can be much thinner. usually one side of turcite is acid etched so glue sticks better. its far more sophisticated then many realize.
 
I'm fully aware of the challenges, and I'm quite certain it is not turcite or other types of "filled" PTFE, it looks and feels like pure PTFE, on couple Fadals I've seen around here, turcite/rulon seems to be quite thick, there are obvious signs of epoxy (or other type) adhesive used to bond it to CI, and even after it was machined/scraped and after decades of neglect it is over 1mm thick, but on this HLV-H (and as far as I could find other people talking about this subject), the material is indeed pure PTFE sheet, and final thickness is very close to what I see on my machine, I haven't torn it off completely, but so far I haven't seen obvious signs of glue used to hold it, so one guess is that it might have been a cyanoacrylate glue to hold it, which supposedly could be used with etched PTFE and the right kind of primer.
One person suggested that originally it was glued thicker, fly cut and scraped to fit, I'll take a closer look at the remnants on this machine to look for scraping signs, which should be there, since the CI gib that rides directly against the steel dovetail does show scraping marks, worn, but they are there, but I didn't see any on the PTFE sheer, not on the top piece, nor the far dovetail. I don't exclude the possibility of the gib being tampered with though. Thankfully the dovetails don't have the typical wear ridge, they actually look quite good considering the condition of the top surface, which was probably due to excessive use of sand paper, which I found lots of small pieces in the cabinet and other recesses of the machine... way wipers were a distant memory, some pieces were still left under the screws on the tail stock side of the carriage.

The machine in question would have otherwise be most likely parted out and scrapped, things like lever collet closer, change gears at the end of the threading gearbox and feed motor were already missing, top slide has been "adjusted" with a steel hammer more than a few times, the thing has endured some tough time in the hands of French machinists which didn't seem to give any love to it, so as far as I'm concerned, any effort in trying improving it over leaving as is in fear of making it worse, is overall positive for it.
p.s. The idea is to keep the machine, not just prop it up, slap some fresh paint on and sell to some unsuspecting victim.
 
a lot of turcite is machined and not scraped and its milled smooth enough you could easily think it was ground.
.
there are "tape" out there, some various materials like uhmwpe that some maintenance person might put on as a quick fix. adhesive already applied in a roll, although how good the adhesive is is hard to say. its right up there with aluminum foil tape that a maintenance person might apply as a quick fix. sometimes it works ok and sometimes does not last long
.
teflon normally doesnt glue that well unless treated like acid etched. part of it being slippery and not much sticks to it also makes teflon hard to apply.
.
uhmwpe (polyethylene) is often confused with teflon
.
also have used a fiberglass tape with teflon coating. used on conveyor side shoots so boxes move along easier. its tough cause its fiberglass, only outside is teflon coated
 
I haven't torn it off completely, but so far I haven't seen obvious signs of glue used to hold it, so one guess is that it might have been a cyanoacrylate glue to hold it, which supposedly could be used with etched PTFE and the right kind of primer.

It might be a stupid question but can you tell if the underneath surface has been etched, after you've torn it off is the back in good enough condition to see what the surface might have been like?

And just a warning, if you do glue on something thicker and machine it down using a fly-cutter or similar, PTFE is slightly compressible as well as slippery so the cutter (unless it's extremely keen) will skid over the top and you will end up somewhere between 0.005" and o.010" over size, the effect get's worse the smaller the cut you take so after the finishing cut the dimensions end up wrong. You may know this already, sorry if you do
 
i machine turcite with uncoated honed inserts made for aluminum (sharp).
.
coated inserts that leave a mirror finish on cast iron are often dull or edge rounded to apply a type of burnishing action. when used on plastic they often push material and leave burr at edges of mill pass often sticking up many .001", that is new out of the box they are not sharp enough to bite into a soft material and its not good to be pushing the plastic surface around
 
here are few pictures of the sad carriage, lighter patches have already delaminated, that one pic shows embedded dirt/grit in the leading edge of the teflon piece (that is a mm scale btw), and the pic where I hold a corner up, that corner I tried to lift to see the bond holding power, and it felt like taring off a good masking tape, it isn't sticky, teflon face looks matte, probably a sign of etching

talked to a teacher in local tech uni that does some material testing research, and he agreed to do some comparative compression tests on the worn piece still glued to the carriage, and the replacement material I ordered, I ordered both the plain teflon sheet (with one side already etched) and the adhesive backed variant, I'm curious how spongy the adhesive backed one will be compared to the original and the replacement

tried touching it with soldering iron, it wouldn't melt even at 400C, that is the max the iron would go to, so it is quite safe to assume it is pure teflon

one thing I forgot to mention, the place where the carriage dovetail faces meet, on the far side, there is a relief cut there, and the top teflon piece was "hanging over" into this relief, meaning - it had no support when it was glued, measured thickness of that overhung material - basically the same as the scored/worn portion, so I'm starting to think it might have not even been fly cut, because the cutter definitely wouldn't have cut that unsupported overhung teflon, should have been thicker if there was any machining done

I'll update the thread after the load tests

IMG_20190305_153800.jpgIMG_20190306_105102.jpgIMG_20190306_105110.jpgIMG_20190306_105137.jpg
 
Have no idea if it would work (I suspect not), but I buy and apply self-adhesive Teflon sheets for re-surfacing microscope stages. The stuff is very sticky -- once set in place only a lot of heat and a razor blade at the bond line seems to disturb it. The point being that the makers of this stuff seem to offer an adhesive, in a fairly controlled thickness, that sticks.

I've bought this stuff in sheets from (if memory serves) from .008" to .040". I'm not at all sure it would hold up under a carriage - indeed I doubt it -- but sheets are cheap enough ($30 or so a square foot) that someone might want to try this??
 
talked to a teacher in local tech uni that does some material testing research, and he agreed to do some comparative compression tests on the worn piece still glued to the carriage, and the replacement material I ordered, I ordered both the plain teflon sheet (with one side already etched) and the adhesive backed variant, I'm curious how spongy the adhesive backed one will be compared to the original and the replacement

tried touching it with soldering iron, it wouldn't melt even at 400C, that is the max the iron would go to, so it is quite safe to assume it is pure teflon

one thing I forgot to mention, the place where the carriage dovetail faces meet, on the far side, there is a relief cut there, and the top teflon piece was "hanging over" into this relief, meaning - it had no support when it was glued, measured thickness of that overhung material - basically the same as the scored/worn portion, so I'm starting to think it might have not even been fly cut, because the cutter definitely wouldn't have cut that unsupported overhung teflon, should have been thicker if there was any machining done

I'll update the thread after the load tests
Looking at how flexible it is, and it won't burn, it's unlikely to be filled, even if it is and you use pure it will still work, it just won't last quite as long. If there's an overhang that's still the same thickness it's not been machined. Can you tell if there's evidence of glue on the back of the overhanging piece? if there is it might mean it's been replaced in the past with an adhesive backed sheet

you could get some adhesive and try gluing a small piece of the etched to a scrap piece of metal as well as a small piece of the adhesive backed, then measure the height with a depth gauge to check the glues don't raise it up to much. Try to pull them both off, use which ever is harder to pull off, (if it's stuck better than the old PTFE sheet was, if not you'll have to rethink)

DMF_TomB said:
i machine turcite with uncoated honed inserts made for aluminum (sharp).
.
coated inserts that leave a mirror finish on cast iron are often dull or edge rounded to apply a type of burnishing action. when used on plastic they often push material and leave burr at edges of mill pass often sticking up many .001", that is new out of the box they are not sharp enough to bite into a soft material and its not good to be pushing the plastic surface around
Thanks for the tip, I tried it - beats using HSS Steel and honing the edge with an oil stone :)
 
Watching this thread for recommendations as to where
to buy this Teflon sheet that is able to be glued
or stickied to the carriage. I have an HLV-H that
the Teflon sheet is coming loose as well. Please
post again when you find a source for material that
is suitable.

Thanks.
-Doozer
 
I found this site via google search - ETCHED PTFE SHEET STOCK - Order Lab Supplies Online & Save , they also responded to my email quite quickly, I haven't placed an order yet though

First I'll test out the Permabond TA4611 glue, should be here next week, it supposedly works on unetched PTFE, if it does, I have already ordered some sheets from asian sellers on ebay which should be here soon as well, if the glue works on the un-etched PTFE, I'll stick to the cheap asian PTFE, if not, will place an order at scicominc.com, shipping will probably cost me more than those PTFE sheets :(

I did try Loctite 770 (polyolefin primer) for gluing low energy plastics, and it seems to work, but not all CA glues I have performed the same, "rubber reinforced" CA worked much better than regular CAs I tested, in fact, the rubber filled CA stuck to the PTFE piece when I glued it to a steel substrate, meaning when I tore the PTFE off, the glue residue was almost all on the PTFE piece, nothing on the steel (and it was cleaned properly), other CA glues stuck to the steel better but the bond with primed PTFE was much weaker, when I tried to peel the rubber filled CA test piece off of the steel, it held pretty much the same as the yet un-peeled pieces on the HLV-H carriage, suggesting that this is what they probably used at the factory, but I think it will be quite difficult to glue such a large piece using the CAs I have, they cure nearly instantly when pressed thin enough, so getting a good level bond might be complicated, that Permabond 2 part acrylic has some working time, not a lot, few minutes, but I figure I will have a much better shot using that than the CA, I just hope it sticks to the un-etched PTFE well enough...

I'll update once the Permabond stuff arrives and I'll have time to do some tests with it
 
I did have a material once for this purpose Also white I do not think it was PTFE
The back had a hairy surface to improve bonding
Do you think you can hold the thickness of the glue in the tolerance that you need
I would keep it in the back of my head that I need to scrape it anyway

Peter
 
I did have a material once for this purpose Also white I do not think it was PTFE
The back had a hairy surface to improve bonding
Do you think you can hold the thickness of the glue in the tolerance that you need
I would keep it in the back of my head that I need to scrape it anyway

Peter

I tried heat on a piece I peeled off, and it wouldn't melt at 400C, it feels (cuts with a scalpel) like PTFE, glues (meaning nothing wants to stick to it) like PTFE, looks like PTFE, so there is an argument to be made it is PTFE :)

when I peeled off the piece, the back side was not semi glossy like virgin PTFE materials usually are, it was smooth and matte, I presume it was etched as a preparation for bonding

regarding the glue, I ordered some extra for testing, I plan to use something alike a notched trowel to spread the glue in even lines so air can escape and when pressed it should flow and make (hopefully) an even thickness film, that is the plan anyway

the really difficult part it seems will be to find a place that can grind the top of the dovetail to remove the scoring marks, probably 0,1mm would need to come off, there are only ex soviet era machines around here, no machine building was really done in the country, and I doubt those might pop up somewhere around here would be in a condition to hold even 0,05mm over the 1050mm length of the dovetail, there used to be a machine building plant in Lithuania in soviet times, but I have no contacts in Lithuania at all, will have to do some digging...

edit: I just realized I posted the wrong link, same site, but the product I was looking for was "film" not "sheet" - ETCHED & ADHESIVE BACKED PTFE FILM - Order Lab Supplies Online & Save
 
Hi,

Did you find a solution to your PTFE problem? I would love to know as I am in the same boat. I just bought a HLV-Kl1 and need to replace the PTFE. I'm based in the UK.

Kind regards,

Alex
 
I have, I bought 1.5mm turcite from far east fleabay, couldn't find a reasonable source closer to EU, the seller couldn't ship epoxy due to pandemic conditions at the time, so I got Araldite from a UK seller, expensive, 180EUR for 1+0,4kg and used maybe 100gr of the mix

machined the saddle for the thicker epoxy-turcite, had to take aprox 1mm off of the horizontal face and the dovetail (that would leave me with 0,4mm extra turcite to machine off before scraping), glued it up, machined down close to size and scraped for final fit, still have to do the oil holes and channels in the turcite, one oddity about this turcite was that HSS fly cutter dulled instantly on it, tried 1000rpm (at ~120mm diameter) and then resharpened and same thing at 200rpm, took a random brazed carbide lathe tool bit and ground that to fit and it did the job with no indication of any wear at all, when I red about machining turcite here and couple other places, people seemed to do fine with just a HSS cutter...

I'll make couple more detailed posts later
 
first a disclaimer :D

this is not HOW TO, but rather how I did it considering the circumstances and equipment I have, I especially don't recommend lapping the dovetail, it is a long and slow process and that diamond grit and slurry is very messy and a pain to clean up

so here goes (writing from memory and few notes I took, so I may miss something), the dovetail was in quite poor shape, when I got it it measured 22.275mm at the ends and 22.255 in the middle (microns are a bit of guesstimate from judging the micrometer sleeve scale, I don't have vernier scale on the 0-25mic, I used that decimal to note on which side of the hundredth of the mm I am)

I made these CI lapping plates, they are around 40mm thick, 2 holes on the back side to be able to drive them with the vertical spindle, I used the quill to engage them, so if anything bad starts going on, I just lift the quill and everything stops. 300rpm and 250mm/min feed, had to stop and relocate the dovetail on the mills table because X axis has only 630mm of total travel.

I tried mineral spirits to thin down the diamond paste, but I had couple instances where cold welding happened on the face of the dovetail and the raised bit scarred the lapping plate (circular grooves on the lapping plate), after this happened I relapped the scarred plate on the 2 other other ones to flatten it, added some oil to the slurry, didn't help much, then switched to wd40 as the thinner for the diamond paste and it seemed to solve the cold welding issue.

at first I tried 80-100 micron diamond paste, had to put quite a lot of pressure on the quill to get it to cut, later switched to finer paste and it seemed that the cutting action and material removal overall went noticeably faster with 20 micron paste slurry, when I had 95% of the grooves out I switched to 5 micron paste and finished it, the final thickness was 22.210 +/- couple microns, 99% of all the wear grooves on the dovetail are gone now, took 12-14 hours total maybe (2 days basically), could probably do it in half the time, a lot of it was trying to get the lapping process down

one pic shows numbers on the dovetail, those are decimals after the 22.
this was after couple passes with the coarse grit, the middle (where the deep grooves were) cut down to .215 basically instantly (that low spot is towards the operator) and then I spent basically 90% of the time to get the ends down to this level, finished it off with hand lapping in the long direction to get most of the swirl marks out

pictures:
a1.jpg a2.jpg a3.jpg a4.jpg
a5.jpg

P.S. regarding the lapping plates, if I had to make new ones, I'd cut wider grooves, I did these on a vertical bandsaw and the width was dictated by the blade, and during lapping it seemed that the width of the groove could have been a bit greater, to help manage the slurry and cut material
 
one the dovetail was done, and the turcite and glue arrived (Araldite AV 138 M-1, hardener HV 998-1), I did some testing on how to spread the glue to try and eliminate any air, and to see what the glue thickness would be, I took a regular steel spatula and made V shaped grooves in it spaced 5mm apart, cut a test sample and glued it up on a piece of HDPE plastic (so it wouldn't stick), buttered both the hdpe and the turcite test piece, the result was no air pockets and glue thickness of 0.2mm

one pic shows a strip I cut from the test piece and I bent it glue face outwards to see how well the glue stuck to the etched turcite, and while the epoxy cracked, I couldn't tare the cracked pieces off of the turcite - so that was another check done

and since I now knew the total thickness of the glue up, I could machine the saddle to make room for the thicker turcite instead of the nylon/teflon/whatever was on there before

I wrote earlier about the trouble I had with the HSS cutter to machine this turcite, the same HSS cut the 1mm off of the horizontal CI face 0.25mm per pass no problem, with no resharpening, but dulled instantly on the turcite, the brazed carbide lathe tool bit I made the next cutter from solved that problem

then it was just a matter of scraping the horizontal face, the print was a bit "fat", that was the last print I took and overdid with the prussian blue a bit, hoping it will be easier to take picture, between the passes I measured the height of the saddle over the dovetail, trying to get all 4 corners to the same height

when that was done I could machine the 60 degree face, machining it was a bit tricky, I had a 60 degree HSS dovetail cutter I machined the CI face with, but that wouldn't work on the turcite, so I had to tilt the head of the mill, extend the quill to max, and then barely had the clearance to make it work, but it did, while I was at it I made a 60 degree prism to be able to measure the scraping progress (measured against the back face of the saddle), when I was parallel there I started to print it off of the dovetail to get full bearing (my "60" prism wasn't exactly 60) and started to use the original gib to see how much I still needed to take off of the 60 degree face turcite, when I took enough off to be able to put the gib fully in, I stopped and did a check to see deflection of the leadscrew while opening and closing the nut, and it was within 0.05mm as far as I could tell and I called it done, as mentioned, still need to do oil holes and grooves

one off thing with the oil holes, there were plastic inserts there to receive the copper or brass oil tubes from the metering valves in the oil gallery at the back of the saddle, and I remember reading somewhere that the plastic inserts were meant to come out flush with the original teflon, so the oil pressure would move the oil right down the feed grooves, and hopefully prevent it pushing in between the teflon and the CI it was glued to, but in case of my machine - the plastic inserts were recessed well into the CI, maybe 1~1.5mm below the CI surface... not quite sure if I need to do anything about that yet

I used some vacuum bagging film I had (tough plastic that glues don't stick to) to cover the dovetail while gluing up the turcite, taped the film down, put the glued up saddle on, put some weight on the saddle, few steel pieces I had, maybe 40kg total, and then used the gib to put pressure on the 60 degree face and couple clamps just to make sure, and it seemed to work out well (as far as I can tell new anyway, this is my first time doing it...)

pics showing the process, forgot to mention - I did rough up the fly cut CI surface with 80 grit sand paper
b1.jpg b2.jpg b3.jpg b4.jpg b5.jpg
 
Excellent work. Im very grateful to you for sharing this! So you lapped the whole bed? That's a very brave move! How are you dealing with the change in tailstock height? I've just measured my dovetails and I've got 22.295 right up by the headstock (no wear) and 22.28 in the most worn spot

How did you measure the leadscrew deflection? I dont have decent machining capabilities where I am so I'm thinking of buying the material close to final thickness and hope I get it close enough to the correct build up after glueing to be able to just scrape it in.
 








 
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